Where We Left Off: Clarke (Eliza Taylor) took the Flame and went to the City of Light to find A.L.I.E.'s (Erica Cerra) kill switch. A.L.I.E. tried to dissuade Clarke by revealing that radiation from nuclear plants is making Earth uninhabitable, but Clarke pulled the switch anyway. Bellamy (Bob Morley) admitted he had gone to the wrong side and Octavia (Marie Avgeropoulos) killed Pike (Michael Beach).
What's Next: Unable to stop the nuclear meltdown, the only thing the people on Earth can do is figure out how to survive. Unfortunately, it soon becomes clear that there's no way to save everyone. This dire situation will throw everything into chaos, with old alliances breaking down and new ones being made. "Back in the old days, you could tell your enemy or you could tell your friend by the uniform that they were wearing or the clan or tribe that they were wearing, but you can't do that anymore," Adina Porter says. "When land is scarce, war happens."
Despite all this, love is in the air between Kane (Henry Ian Cusick) and Abby (Paige Turco), Murphy (Richard Harmon) and Emori (Luisa D'Oliveira), and Monty (Christopher Larkin) and Harper (Chelsey Reist). And once again, Clarke will have Bellamy by her side as she's forced to face another round of impossible choices. However, Octavia will go to her darkest place yet, devoting herself fully to the life of an assassin, much to Indra's (Porter) glee.
And though the City of Light is officially gone, the Flame -- and the minds of all the commanders inside it -- still exists. However, there are no more Nightbloods, a fact that is crucial to a new character this season, a female Nightblood scout, who finds herself questioning her religion following the events of Season 3. Roan (Zach McGowan) will return as a season regular as he sets out -- with the help of Echo (Tasya Teles) -- to lead not just the Ice Nation, but every survivor. Luna (Nadia Hiker) and Niylah (Jessica Harmon) will also return.