I feel the sun on my face. I see trees all around me, the scent of wildflowers on a breeze. It’s so beautiful. In this moment, I'm not stranded in space. It's been ninety-seven years since a nuclear apocalypse killed everyone on Earth, leaving the planet simmering in radiation. Fortunately, there were survivors. 12 nations had operational space stations at the time of the bombs. There is now only the Ark, one station forged from the many. We’re told the Earth needs another 100 years to become survivable again. Four more space-locked generations and man can go home, back to the ground. The ground — that’s the dream. This is reality. Reality sucks.
Set in an indeterminate year in the distant future, 97 years after a nuclear apocalypse has devastated the surface of Earth, the only survivors were approximately 400 inhabitants of 12 national space stations that were in orbit at the time.
On Earth, the 100 discover Earth is in fact, livable. When Clarke soon realizes they've landed on the wrong mountain and a radiation soaked forest sits between the 100 and their next meal, Clarke gathers a small group to head for Mount Weather for food and supplies. Clarke and the group quickly discover Earth is filled with wonders and dangers of all sorts. Meanwhile, the rest of the 100 stay near the landing site and one of their own makes plans to ensure the Ark believes the 100 to be dead.
Back on the Ark Chancellor Jaha has been shot, leaving Abigail Griffin to try and save his life at all costs. Meanwhile, with the Chancellor dying, his second in command, Councilman Kane, takes charge. Councilman Kane is a man who doesn't believe in mercy in a place where all law breaking is a capital crime.
In 2149 CE, Clarke Griffin draws a picture on the floor of her room on the Ark. Two Ark Guards enter her room, one of whom orders Clarke (Prisoner 319) to face the wall. One of the guards opens up a metal box containing wristbands. Clarke mistakes the wristbands for the device that will execute her and expresses panic due to the fact that she doesn't turn eighteen for another month. When the guard orders Clarke to remove her watch she protests, due to it being the last she owns of her father's. The guard grabs for her wrist and Clarke fights back. Overcoming both guards, Clarke escapes her cell. Outside of her cell, Clarke sees guards escorting juvenile delinquents. Clarke’s mother, Abigail Griffin, appears and hugs her frightened daughter. Abigail reassures Clarke that the Delinquents aren't being executed and informs her that they are being sent to the ground instead. A guardsman shoots Clarke with a tranquilizer.
When Clarke awakens she finds herself on a dropship headed for Earth. Clarke discovers that and old friend who betrayed her, Wells Jaha, is also on the drop ship after he got himself arrested in order to protect Clarke. When they hit Earth’s atmosphere a message from Chancellor Jaha appears and explains to the 100 that they are being sent down to Earth because they are expendable but that if they are co-operable, their crimes will be forgiven.
On the Ark, citizens demand answers for the launched dropship. Callie Cartwig explains that they can't confirm or deny anything at the time and walks away.
On the drop ship, Clarke learns that their drop site is a military base called Mount Weather. While watching the video, Finn Collins gets out of his seat and performs aerial stunts near Clarke and Wells. Two other delinquents follow his lead and try to get out of their seats, despite Clarke's protestations. Finn points out that Clarke has been in solitary for over a year and Clark, annoyed, points out that he wasted three months of oxygen on an illegal "spacewalk". Moments later, the parachutes deploy, sending the two delinquents and Finn flying.
On the Ark, Callie, Marcus Kane, and Commander Shumway learn from Sinclair that the drop ship has had a total system failure and that they're off-course. Kane asks about communications and Sinclair informs him that there's no way to contact the delinquents; the 100 are on their own.
On Earth, the drop ship comes in too fast. Wells worries because the retrorockets didn't fire when they were supposed to. He then goes to apologize for getting Clarke's father arrested and, eventually, executed. Clarke is hostile toward Wells and declares her hatred for him. The retrorockets fire, interrupting them, and the drop ship lands on Earth.
Monty Green, strapped to the wall, observes that there is no machine hum and the crash must have cut off the Ark's communication to the 100. The delinquents begin to recover from their landing and unstrap themselves. Clarke gets out of her seat and checks on one of the two delinquents who followed Finn out of their seats. Clarke asks if the other is breathing. Finn exchanges a look with Clarke, indicating that both delinquents are dead.
Clarke descends from a ladder and stops Bellamy Blake from opening up the drop ship door due to the fear that the air could be toxic. Bellamy ignores her, explaining that in that case, they would all be dead anyway. Bellamy goes to open the door when a young woman hesitantly calls out his name. A delinquent shouts revealing the young woman as Octavia Blake, Bellamy’s sister and the girl the Ark found hidden in the floor illegally. 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. The rest of the Delinquents smile, shout, and cheer as they race out of the drop ship to explore their new world. Clarke jumps onto the ground and her face lights up 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.
On the Ark, Kane informs everyone that the 100 have landed but the communications are down. It is only thanks to Abby’s wristbands that they know what is happening on Earth. Abby informs Kane that so far they have two dead kids; they show up as dark tiles. Abby and Jackson theorize the two were killed on impact because they went black at the same time they lost communication. Kane deduces that if it was radiation that killed them, there would be more fatalities showing up already. Kane is curious about what Abby thinks all of the red means. Abby explains it as either injuries sustained in the landing or the kids' excitement to be there.
On Earth, Clarke plots a route to Mount Weather. Clarke decides they need to worry about getting to Mount Weather. She shows him the path they need to take. Wells asks her where she learned to do that. When Clarke doesn't answer, Wells realizes her father taught her. Jasper approaches and playfully flirts with Clarke. Wells roughly grabs his arm and pushes him away. John Murphy sees this and confronts Wells, stating Jasper is one of them. Wells tries to talk Murphy down but is interrupted by Bellamy.
Wells explains that they need to find Mount Weather. Octavia mocks Wells and Clarke because they are considered privileged. Clarke doesn't let this stop her, instead explaining that if they continue to wait, they will go hungry. Bellamy proclaims Clarke and Wells should go, while the rest wait for them to return with food and supplies. Wells tries to make Bellamy understand that they all need to go. Murphy shoves Wells, trying to start a fight, while John Mbege holds Clarke back. Before the two can fight, however, Finn intervenes and tells Murphy to wait until it is a fair fight. Octavia approaches and suggestively hints for Finn to save her next. He flashes Octavia a smile before walking away. Clarke goes to check on Wells while Bellamy approaches his sister and gives her a look. Octavia shrugs, and says, "he's cute". Bellamy expresses concern that Finn is a criminal, but Octavia points out that they are all criminals. Bellamy explains that he came to protect her, but Octavia doesn't want his help. Bellamy tells her he can't stay because he did something that the council would kill him for but refuses to tell Octavia what he did. Clarke checks Wells' injured leg as Finn approaches them and asks when they leave. Clarke tells him they are leaving right away before turning to Wells to explain when they will be back. Finn recruits Jasper and Monty to the group and Octavia invites herself along for the journey even as Bellamy tries to stop her. When Clarke spots a scuff mark on the side of Finn's wristband, she scolds him and tells him that the wristbands transmit vital signs to the Ark. If they take them off the Ark will think they are dead, unknowingly giving Bellamy an idea. Clarke sets out for Mount Weather with Finn, Jasper, Monty, and Octavia.
Walking through a lush forest, the group takes their time admiring Earth. Clarke observes that there are no animals, and concludes that there must have been enough radiation to wipe them out. They continue on walking and Monty and Jasper reveal how they got busted for stealing from the Ark's garden and forgetting to replace what they took. Jasper asks Octavia what she was arrested for of which she replies "for being born". Clarke motions for everyone to join her. In front of them is a deer grazing in the field. Finn snaps a twig and the deer turns to them, shocking the group with its two heads.
On the Ark, Abigail Griffin and her assistant, Jackson, operate on the dying Chancellor. During the operation, the Chancellor begins to awaken. Abby orders the nurse to increase the anesthesia. However, the nurse is hesitant and Jackson notes that they have used too much blood and anesthesia and is worried about breaking the law. Abby increases the anesthesia regardless, knowing it is illegal.
In another part of the Ark, Commander Shumway notifies Kane that the Chancellor is still in surgery. He also informs Kane that they have identified the shooter as Bellamy Blake. Commander Shumway mentions to Kane that his motivation for getting to Earth was clear: his sister. Kane remembers that her mother had kept her hidden for almost 16 years, a near record. Commander Shumway urges Kane to resume position as Chancellor and start reducing the population. Kane is focused on finding out who helped Bellamy Blake get on the drop ship.
On Earth, Wells is confronted by Murphy, who asks him if he found water. Wells tells him that he has not and invites Murphy to join him when he goes back out. Wells notices that Murphy engraved “FIRST SON FIRST TO DYE” on the side of the dropship. Murphy explains that his father begged for mercy before Wells’ father floated him. Instead of being intimidated by Murphy, Wells mentions that Murphy spelled die wrong and leaves. Bellamy approaches Murphy and John Mbege and tells them that if they plan to kill someone it's not a good idea to announce it. Bellamy convinces Murphy and Mbege that they will not be forgiven for their crimes or live a better life once the Ark comes down. When Murphy asks how they stop it, Bellamy tells them to take off the wristbands to make the Ark think they're dead so the rest of the Sky People won't follow the delinquents to earth. Bellamy offers Murphy and Mbege positions to help him run things around camp.
Back on the Ark, Abby notices some of the wristbands are going dark. Kane believes it to be radiation but Abby counters this, saying that that is not how radiation works.
In the woods, Clarke tells the group the reason the 100 were sent to Earth after ninety-seven years is because the Ark is dying and only has three to four months of life support left and that is the reason she was locked up in solitary and her father was floated for it. Octavia then takes off to the edge of a stream and strips off her pants as Jasper ogles her. Octavia leaps into the water below. Luckily, the water is shallow, for none of the 100 can swim. Other than Clarke, they all start taking off their clothes to join Octavia. Jasper spots something in the water and shouts at Octavia to get out of the river. Octavia is suddenly pulled under by a river snake. She comes up a bit farther downriver, screaming. Clarke, Monty, and Finn toss a boulder into the water to distract the river monster but Octavia is unable to swim to shore. Jasper jumps in and grabs her just as the creature comes back and he is able to pull Octavia to shore in time.
Later that night, back at the Camp, Wells watches as Mbege and Murphy remove Fox's wristband and toss it into a bonfire. Wells explains that the delinquents will not be able to survive on their own. Bellamy goes on to say that there are no laws on Earth and they can do "whatever the hell we want". It suddenly starts raining to the delight of the Delinquents and Wells tells Bellamy they need to collect the water. Bellamy tells him, "whatever the hell you want."
Up on the Ark in the Earth Monitoring Center, Abby observes that ten more tiles have gone dark. Jackson realizes that the delinquents found water. Commander Shumway enters with Kane and publicly arrests Abby for exceeding the maximum medical supplies allowed per patient. Abby takes it in stride, explaining that it was worth it to break the law in order to prevent Kane from becoming Chancellor. Kane, as Chancellor, finds Abby guilty and then sentences her to death, scheduling her execution for the following morning. Kane then has her locked in Clarke's old prison cell where she sees all of the drawings Clarke made over her year in solitude and cries.
Clarke awakens while it is still dark out. Jasper, Monty, and Octavia are asleep behind her as she sits up and witnesses the trees and plant life aglow with bioluminescence. Finn approaches her with a leaf filled with water for her to drink from. He then shows her some tracks in the dirt and says he thinks there might be monkeys.
On the Ark, a heartbroken Callie approaches Kane in his quarters about Abby's sentence, but he does not budge.
Wells is woken from his sleep by Bellamy's hand over his mouth and a gun pointed in his face. Bellamy takes him away from camp in order to explain that he needs the Ark to think he is dead. He asks him to take off the wristband. Wells refuses and Bellamy apologizes before Murphy and Mbege hold Wells down and forcibly remove his wristband.
Up on the Ark in Clarke's old room, Abby stares out into space as a guard opens her door and tells her it is "time". She is led to an airlock where Commander Shumway and Kane wait. Callie hugs her goodbye and Abby walks into the airlock with Shumway sealing it behind her. Abby tells Jackson to talk with Sinclair in Engineering about figuring out how to reverse-engineer the wristbands to communicate with the delinquents. Kane gives the nod to Shumway to float Abby but is told to stop by Chancellor Jaha, who has awakened from his surgery. He pardons Abby, who walks out of the airlock and orders Jaha back to bed before she leaves with Callie. Kane informs Jaha about the 100.
Down by the river, Finn is holding onto a vine, about ready to swing across the river to the other side. Jasper tells him to let go at the apogee. As Finn is about to take off, Jasper asks if he can go first so he can impress Octavia. Finn agrees and Jasper goes soaring across the river, letting go as he screams "apogee" and lands safely on the other side. They all begin cheering and Clarke prepares to go next. Jasper picks up a sign reading, "Mount Weather," and holds it above his head, telling them they did it and reached Mount Weather. He is suddenly knocked off his feet and propelled back, pinned against a tree with a giant spear protruding from his chest. Clarke, Finn, Monty, and Octavia all duck down in fear as they realize they are not alone.