After losing nearly all food supplies through a fire, the remaining "100" are forced to go hunting despite the constant threat of the Grounders. Clarke and Finn are caught up in the aftermath of bombing the bridge and may have to pay a high price ... Meanwhile on the Ark: Councillor Kane goes to great lengths to find and save survivors in the repercussion of major destruction.
After one of the 100 return to camp with a virus, getting many of them sick, Octavia, Finn, Jasper, and Raven devise a plot to try to hold off the grounders from war.
Both the ARC and the 100 celebrate Unity Day. The ARC is devastated by first an explosion, then an attempted coup. Meanwhile, on the ground, Clarke, Finn, and Octavia set up a meeting with the grounders.
Clarke and Finn grow closer as they try to communicate with the Ark. Meanwhile, Bellamy maintains order within the group.
100 young criminals that have been living in space on The Arch have been sent to Earth to test if it has become inhabitable after 97 years of being abandoned after a nuclear war.