1. Echoes

Complete story — includes the ending

This episode's plot summary may be too long or excessively detailed. Please help improve it by removing unnecessary details and making it more concise. ( September 2020 ) ( Learn how and when to remove this message ) Clarke confides in Bellamy about A.L.I.E.'s warning of the nuclear power plants melting down and the human race surviving only six more months. In the aftermath of the battle, it turns out that the people Lexa killed to protect Clarke in the City of Light are actually dead, leading the people of Polis to declare both Wanheda and Skaikru their enemies; Echo leads the Ice Nation warriors against Skaikru and begins to take the city by force. To stop her, Clarke and Abby manage to save King Roan from his bullet wound. When Roan awakens, Echo attempts to convince him to kill Clarke, but Clarke gives Roan the Flame; he declares himself ruler of the thirteen clans until the Flame chooses another commander, and he announces their peace with Skaikru. Murphy and Emori run away from everyone to be together; Clarke, Bellamy and Jaha leave Polis and return to Arkadia to decide their next move in their fight against the radiation that's coming. Elsewhere at Arkadia, Raven attempts to determine exactly what kind of damage the radiation will deliver while Jasper's suicide attempt is unknowingly interrupted by Monty. Using Arkadia's sensors and historical records, Raven determines that A.L.I.E. was telling the truth as radiation levels are already beginning to rise and the power plants were only designed to last for one hundred years without maintenance. At the same time, in Egypt, a radioactive pyroclastic wave kills two people, an effect of the approaching apocalypse.