Clarke and Octavia become good friends during Season One, working and overcoming many obstacles together. After Octavia finds out that Clarke knew ahead of time about the bombing of Tondc in Season Two, however, Octavia ends their friendship.
After the battle at the Camp, Octavia and Clarke are reunited again in Season Two when Octavia arrives at Camp Jaha with Bellamy in Human Trials. Octavia leads Clarke and Bellamy to Tondc where they discover Finn has massacred most of the village. In Long Into an Abyss, Clarke helps Octavia with Lincoln when they discover he has been turned into a Reaper. Octavia discovers Clarke knew ahead of time about the missile landing on Tondc in Bodyguard of Lies and dissolves their friendship. They get in an argument again When Clarke arrives at the Mount Weather intake door in Blood Must Have Blood (Part 2). After the take-down of Mount Weather, Clarke leaves Octavia behind along with the rest of the Delinquents at Camp Jaha.
In the Pilot, Clarke descends from a ladder in the drop ship and stops Bellamy Blake from opening up the drop ship door, explaining the air could be toxic. Bellamy tells her that if the air is toxic they are all dead anyway. Bellamy goes to open the door when a young woman hesitantly calls out his name. A Delinquent shouts out the young woman is Octavia Blake, Bellamy’s sister and the girl they found hidden in the floor. This angers Octavia, causing her to try attacking the Delinquent who made the comment, however, Bellamy stops her. Bellamy offers Octavia something else for people to remember her by: the chance to be the first human on the ground in over 100 years. This excites Octavia. Bellamy opens up the drop ship door and Delinquents experience their first breath of fresh air. Octavia steps out of the drop ship and savors the feeling of being on Earth. Bellamy blocks the others from leaving the drop ship. Octavia jumps onto the ground and smiles. Behind her, the Delinquents and Clarke take in the sights of Earth. Octavia throws her fists into the air and shouts in excitement.
Clarke’s excitement is short lived when she realizes they are not on Mount Weather and that a radiation-soaked forest sits between them and their next meal. Bellamy suggests Clarke and Wells go instead while the rest wait for them to return with supplies. Clarke sets out for Mount Weather with Octavia, Finn Collins, Jasper, and Monty. While Walking through a lush forest, Clarke informs them that The Ark is dying. Clarke admits she was arrested because she and her father planned on going public with the information. Nearing Mount Weather, the group finds a river where Octavia decides to go for a swim. Moments later, Clarke and the others watch in horror as Octavia is attacked by a sea serpent. Clarke helps scare off the snake off by dropping a large rock into the water. After their run in with the sea serpent, they try to find another way across the river. The next morning, they find a strong vine that will allow them to swing over to the other side. Jasper crosses first and they all cheer in excitement until he is struck down by a spear. Clarke comes to the realization that they're not alone.
In Earth Skills, Clarke, Octavia, Finn, and Monty flee through the woods after witnessing Jasper getting speared by the Grounders. Monty trips and falls and they see a misshapen human skull on the ground. They hear Jasper screaming and race back to the river bed to find Jasper gone. When they arrive back at camp, Bellamy rushes over to Octavia when he sees she was injured and asks where the food is and what happened. The Delinquents gather around to listen as Clarke explains how the Grounders took Jasper. Later, Clarke approaches Bellamy who is tending to Octavia's injury to get him to join their rescue party for Jasper. Octavia tells Clarke she is coming but Clarke tells Octavia her leg will just slow them down.
In Earth Kills, Octavia hears Jasper screaming from the drop ship and hurries up to the Third Level where Clarke is trying to cut away Jasper's infected flesh. Bellamy tells Clarke she can't save Jasper's life and his screams are making people uncomfortable. Clarke tells Bellamy that this is not the Ark and down here every life matters. Bellamy calls Jasper a, "lost cause," and tells Clarke if Jasper isn't better by tomorrow, he'll kill Jasper. Clarke tells Octavia there is hope. Bellamy tells Octavia to leave with him but she refuses. When Clarke leaves with Finn and Wells to retrieve more seaweed for Jasper's wound, Octavia remains behind to take care of Jasper and protect him from John Murphy who wants to put him out of his misery.
When they return to camp with Atom's body, Bellamy orders them to get Clarke whatever she needs for Jasper as Wells tells Bellamy he'll go dig Atom's grave. Octavia comes running up and Clarke tries to pull her away. Bellamy also tries to stop her but she pushes past him and sees Atom's body.
In the drop ship, Clarke has made a tea from the seaweed and is forcing Jasper to drink it. She tells Octavia that she is sorry about Atom and Octavia says they will have to get used to people dying, but not Jasper. Later, Octavia, Monty, and Finn are passing around the bottle of whiskey when Jasper asks for some. They welcome him back and Clarke comes up, telling him he will have an impressive scar and thanks him for not dying.
In Murphy's Law, after finding a knife and Wells' fingers, Octavia and Jasper take the items to Clarke and Bellamy. Clarke realizes the knife belongs to a Delinquent and that the Grounders didn't murder Wells; it was one of them. Bellamy tells Clarke she needs to keep this quiet because their fear of the Grounders is building the wall that is keeping them safe. Clarke points out the knife belongs to John Murphy and the Delinquents have a right to know that he murdered Wells. Clarke storms out of the tent and confronts Murphy about the knife. She tells Murphy he's going to pay for it and Octavia pipes up that Murphy also tried to kill Jasper. As the Delinquents start lynching Murphy, both Octavia and Clarke try to get them to stop.
In His Sister's Keeper, when Bellamy realizes Octavia has been missing for several hours, Clarke tells him it is because of Octavia that she will help him search for his sister.
In Contents Under Pressure, Octavia assists Clarke with Finn's stabbing when Bellamy, Miller, and Drew drag the Grounder that saved Octavia into the drop ship. Octavia follows Clarke into the room where the Grounder is being beaten and interrogated. This upsets her because the Grounder had saved their lives. Finn's condition worsens when it is discovered the blade was poisoned. As Bellamy, Clarke, and Raven grow increasingly more brutal in the torture of the Grounder, Octavia puts a stop to it by slicing herself with the knife that the Grounder used on Finn, forcing the Grounder to reveal the correct antidote in order to save Octavia's life. Later, Octavia takes over for Clarke and tends to the Grounder's wounds.
In Unity Day, Finn catches Octavia with Lincoln and convinces Lincoln to set up a peace meeting between Lincoln's leader (Anya) and Clarke. Later, Clarke and Finn arrive at the meeting place on a bridge where Octavia is waiting. Clarke realizes it was Octavia who set it up and Octavia tells Clarke that she trusts Lincoln. Unknowingly to Finn, Lincoln, and Octavia, both leaders brought back-up. When a fight breaks out, Lincoln tells them to get back to their drop ship and takes off the other way. Back at camp, Octavia blames Jasper for ruining everything, and she walks away, angry.
In I Am Become Death, after it is discovered that Murphy brought a type of hemorrhagic fever back into their camp, the delinquents start getting very sick. Bellamy is worried about Octavia because she was the first one to find Murphy so he brings her to Clarke and Clarke tells Bellamy that she needs to quarantine her. Once Bellamy leaves, Clarke tells Octavia that she needs to talk to Lincoln to get the cure. Later, when Bellamy falls ill, Octavia takes care of him and Clarke and spends the night tending to the sick as she is immune.
In The Calm, Octavia is working in the Smokehouse with Murphy when Del brings in more wood for the fire. Octavia warns Del that they have too much wood but he decides to ignore her warning. As a result, the Smokehouse ends up burning down. After the fire is out, as they're sifting through the fire, Clarke asks what happened and Bellamy explains that Del built the fire up too much because Octavia told him it was a bad idea. Clarke tells him they need to go hunting because they can't defend themselves if they're starving. Later, after Clarke doesn't return from hunting, Octavia joins the search party for Clarke, Finn, and Myles.
In We Are Grounders (Part 1), Lincoln helps Clarke and Finn escape from the Grounders] and asks them to take Octavia away from The Camp before the Grounders attack. When Clarke and Finn return to the Camp, Finn hands Octavia Lincoln's sword, shaking his head to show that he didn't think Lincoln had escaped the Reapers.
In Fog of War, Octavia and Bellamy go along on Clarke's mission to take out Mount Weather's radio tower. When Abby notices Bellamy and Octavia are gone, Clarke tells her they are trying to find another entrance to Mount Weather.
In Long Into an Abyss, Octavia is sitting in the drop ship where a Reaper Lincoln is once again chained to the walls when Bellamy brings Clarke in. Lincoln manages to break free and attacks them. Octavia hits Lincoln over the head, knocking him unconscious. They get him chained back up and Clarke treats his bullet wound while Octavia tries to give him some water but Lincoln thrashes at her, upsetting her. Octavia leaves the drop ship to get some more water and returns with Lincoln's friend, Nyko. Clarke figures out that Nyko is actually trying to mercy-kill Lincoln and stops him. She realizes that the Grounders have been trying to bring back Reapers and failing and sees it as a possible way to stop Lexa from ordering the attack on Camp Jaha. Finn arrives and Nyko tries to kill him for the massacre in Tondc. When Bellamy attempts to shoot Nyko, Octavia tries to stop Bellamy while Clarke shocks Nyko with a Camp Jaha Guard's stun stick, knocking him out.
Later, after Clarke brings back Lexa to the drop ship to show the Grounders they can cure Reapers, Lincoln's heart has stopped beating again. Abby uses the shock baton to try restarting his heart and Clarke tells Abby to try it again, successfully resuscitating Lincoln. Octavia kisses him, happy to see that he is alive.
In Spacewalker, Octavia is with Lincoln in Camp Jaha's medical facility where he is recovering from being a Reaper. Clarke visits with Abigail Griffin and they ask Lincoln how to negotiate with Lexa in order to save Finn but he says there is no way out of it and Finn must die. Octavia asks what would happen to Finn and Lincoln tells them that because Finn killed 18, he will suffer 18 deaths as a result. Clarke asks how he can say that about his friend and Lincoln tells Clarke that some of the dead Finn had massacred were Lincoln's friends, too.
In Remember Me, Octavia and Clarke journey to Tondc with Commander Lexa where Finn's body is ritually burned with his 18 victims. After Gustus is poisoned at the peace dinner and the Sky People are locked up, Octavia tries to help Clarke when Clarke starts hallucinating that Finn is with them. After Raven is able to hear Jasper's recorded message from Mount Weather, Clarke tells Bellamy he needs to find a way in. Lincoln offers to lead Bellamy through the Reaper tunnels and Octavia wants to go with them but Lincoln tells Octavia she needs to stay behind to help with the alliance.
In Coup de Grâce, after Carl Emerson and another Mount Weather Guard attempt to assassinate Clarke, Octavia fights Emerson, tearing his radiation suit. Indra tells her to "finish it" just as Clarke rides up and stops her, telling Octavia they want to keep him alive and to check for a patch kit for his suit. Octavia digs through Emerson's bags and finds a picture of Clarke and Lexa on horseback, the intended targets. Indra sends a rider to go warn Lexa of the attempted assassination.
Back at Camp Jaha, Octavia asks Clarke if there is any word from Bellamy and that Lincoln is still missing, too. Clarke tells her that Bellamy will get into Mount Weather. Later, Clarke brings Octavia, Indra, and several other Grounders with her to Emerson's airlock where Clarke makes the guard stand down and tells Emerson to get dressed. They take him outside and bring him to the gates where Kane and Abby try to stop her. Abby tells the Ark Guards to get the prisoner back inside but the Grounders behind Clarke step up threateningly. Clarke tells Abby, "you may be the Chancellor, but I'm in charge," and refuses to back down. Kane tells Abby that it is time they started trusting Clarke. Abby finally gives the order to stand down to the Ark Guards and Clarke makes her way through with Emerson. She tells Emerson to deliver a message to Mount Weather and that they have a secret Grounder army that the Acid Fog can't hurt. With the tone generator they got off of Emerson, the Reapers can't hurt them either. Mount Weather has one last chance to let the Delinquents go and the Sky People will let them live. Clarke then releases air from Emerson's oxygen tank and tells him he has to make the eight-hour walk back to Mount Weather in six hours. Octavia asks how this will help Bellamy and Clarke tells her that it will make them look outside for this secret army instead of inside where they might find Bellamy and that Bellamy is the key to everything.
In Rubicon, in Mount Weather, Bellamy is crawling through the air vents trying to find the missing Delinquents. He overhears Cage Wallace asks Emerson about Clarke and Emerson gives him the message that they're supposed to release the Delinquents. Cage then tells Emerson that it doesn't matter because tonight, he is going to drop a missile on Tondc where all of their leaders are meeting. Bellamy asks Clarke if she heard everything through his earpiece and she tells Raven she's leaving for Tondc. Bellamy asks after Octavia and Clarke lies that she's not in Tondc anymore. Clarke rides into Tondc and is greeted by Octavia. She tells Octavia to take her to Lexa and Octavia asks what is wrong. In the woods outside Tondc, a Mountain Man (Whitman) reports back to Mount Weather that Clarke has arrived.
In Resurrection, Octavia helps dig out the survivors after the bombing of Tondc. She tells Abby that she is sure Clarke is okay. Later, Clarke returns with Lincoln and Lexa to Tondc after they take out the Mount Weather sniper. Clarke walks up to Octavia and Octavia tells her she's glad she's not dead to which Clarke replies, "you, too."
In Bodyguard of Lies, in the Grounder camp outside Mount Weather, Clarke approaches Octavia across from a campfire. Octavia confronts Clarke about the bombing of Tondc and asks Clarke to tell her she didn't know it was coming. Clarke tells her she did it to save Bellamy and Octavia tells her that Bellamy would have never agreed to it and would have found another way. Clarke tells Octavia she can't tell anyone and Octavia says she knows; the alliance would break. They are then interrupted by Lexa and Ryder, one of her bodyguards. Ryder tells Octavia to go relieve the southernmost guard position. Octavia tells them Indra expects her to be on a scouting mission with Lincoln. Ryder tells her that Indra will join her there shortly and Octavia walks off. Clarke tells Lexa that Octavia won't say anything and Lexa says she can't be sure of that. After Clarke leaves, Lexa tells Ryder to kill Octavia.
Clarke spots Indra seated near a fire and asks her why she's not on watch with Octavia. Indra tells her she doesn't stand watch and Clarke then asks where Octavia is. Indra tells her that she's with Lincoln, scouting as planned. Clarke then heads off to find Octavia and spots Ryder with an arrow aimed at Octavia. Clarke points her gun at his head and tells him to stand down and come with her and she leads him away from Octavia. Clarke brings Ryder back to Lexa and tells her that Octavia is not a problem. Lexa tells Ryder to stand down and sends him away. Clarke tells Lexa she can't kill anyone she doesn't trust. Lexa says yes, she can. She calls Octavia a threat and Clarke tells her that Octavia wouldn't ever endanger her brother's life. She then tells Lexa that she's a liar and really does have feelings, about Gustus, about Costia, and about the people who burned in Tondc. Lexa tells Clarke that she didn't let her burn. Clarke asks for Lexa to trust her that Octavia is not a threat and then warns Lexa that if she does anything to Octavia, Clarke will tell everyone about the missile. Later, Lexa summons Clarke to her tent to tell her that Octavia has nothing to fear from Lexa because Lexa trusts Clarke.
As the Grounder Army marches on Mount Weather, Clarke wants to take Octavia out of the mines and tries to assign Octavia to the Rear Guard where she'll be safe. Octavia tells Clarke she doesn't take orders from her; she takes them from Indra. She then breaks off their friendship, telling Clarke she only fights this war with her because she wants their friends back. Indra tells Clarke that Lexa is looking for her and Clarke takes off. Octavia and Indra then discuss the Tondc bombing and she doesn't understand why Indra isn't mad at Lexa and Clarke for letting all those Grounders die. Indra tells her it was the Mountain Men who were responsible for their deaths.
In Blood Must Have Blood (Part 2), down in the mines underneath Mount Weather, Octavia is waiting by herself for Bellamy to open the intake door. An alarm sounds and a body is dropped down a chute into a mining cart. Octavia sees Fox, dead from bone marrow drilling. Clarke comes running up, telling Octavia that Lexa and the Grounder army has left. Octavia and Clarke then get in a fight because Clarke is desperate to get into Mount Weather and will bring unwanted attention on them. Suddenly, the door opens and Bellamy appears with Monty, Jasper, and Maya and everybody hugs. Clarke asks Bellamy if he has a plan and he tells her he doesn't, but they can speak to Dante Wallace. Maya's oxygen tank beeps, warning her she is running low on oxygen. They split up with Bellamy, Clarke, and Monty going after Dante while Octavia goes with Jasper and Maya to get Maya to Level 5 before she runs out of oxygen. The next day, after Mount Weather is defeated, Octavia returns to Camp Jaha while Clarke leaves on her own.
In Hakeldama, Indra radios Kane following the massacre and Octavia arrives in his place. Clarke says that she can fix everything if she can talk to Bellamy since if she can convince Bellamy, she is determined he can convince Pike. Octavia helps her get into Arkadia and arranges a secret meeting with Bellamy. When Bellamy betrays Clarke, Octavia comes to her aid and the two escape Arkadia with the help of Kane and Abby.
In Thirteen, Clarke encounters Octavia and Polis and Octavia tells her they need to leave before the grounder blockade is solidified. Clarke is ready to leave with Octavia and goes to say her goodbyes to Lexa while Octavia sets out to find Indra.
In Demons, Clarke, Octavia, Raven, Monty, Jasper, and Bellamy return to Arkadia in search of Lincoln's journal which has information about Luna. However, Emerson slowly captures the delinquents and traps them in the airlock telling Clarke to surrender. Clarke surrenders and Emerson tells her she now gets to endure the same pain as him since she'll be watching her friends die. Clarke makes a quick decision and puts the flame in Emerson's neck killing him and saving her friends.
In Join or Die, Monty, Raven and Harper chose to stay behind in Arkadia leaving Octavia, Jasper, Bellamy and Clarke to search for Luna. They reach the place Lincoln marked in his journal and find nothing there before Jasper discovers they can contact Luna using signal fire. Two boat people arrive and Octavia requests safe passage and she is given a vial. She drinks it and soon falls to the ground. Clarke, Jasper, and Bellamy to drink it as well and awaken in the middle of the ocean on Luna's rig. Clarke offers Luna the flame, however, Luna declines it.
In Red Sky at Morning, Clarke tells Bellamy, Jasper, and Octavia she plans to give Luna the flame by force. Octavia says it's a bad idea but Clarke does it anyway. Luna, however, notices Clarke before she strikes and knocks her down taking the flame from her until they leave. A.L.I.E. and chipped grounders infiltrate the rig and begin chipping the grounders that are there. After a battle, the Flokru bid farewell to their dead and Luna sends Octavia, Clarke, Bellamy, and Jasper back home.
In Perverse Instantiation (Part 1), Clarke and Octavia argue over leadership before Clarke encounters Roan. They stage a plan to enter Polis since Clarke and Roan have a common goal, they both want to give the flame to Ontari. Clarke enters as Roan's prisoner while Octavia, Bellamy, Bryan and Miller plan to attack the chipped soldiers as they come. They then encounter Murphy, Pike and Indra and brand together. However, a chipped Kane soon arrives and shoots Bryan and Pike and the plan fails since Clarke is taken to the Polis tower by Jaha and Abby.
In Perverse Instantiation (Part 2), Clarke successfully unchips her mother using the EMP. Clarke realizes she needs to take the flame to get the kill code herself and Octavia and others agree to protect her when she later determines she needs to enter the City of Light. Later, Clarke is visibly shocked when Octavia kills Pike and walks out of the throne room as if nothing has happened.
Octavia: "I saw you in Tondc before the missile hit. I know you, Clarke. Something's wrong. And then you and Lexa disappear and just happen to survive. Tell me you didn't know it was coming. You let all those people die. You were gonna let me die."
Clarke: "I did it to save Bellamy so that we could win this war. Don't you see that? If we'd evacuated Tondc, Mount Weather would've known that someone tipped us off. They would have found your brother."
Octavia: "No. Bellamy would have never told you to do that. He would've found another way."