Plot summary
The Dark Commander, now in full control of Madi, threatens to kill her if he is deleted from the Flame; without Becca's notebook, Raven is unable to hack the Flame and delete him. To protect Madi, Abby becomes a Nightblood to give the last doses of bone marrow to Russell. After reconciling with Raven, Abby is mind-wiped by Russell and made into the new host for a resurrected Simone. With Russell preparing to resurrect all of the Primes, Gabriel goes rogue to stop him, but can't bring himself to kill Russell and is captured.
Continuing her guise as Josephine, Clarke forces Priya to help her knock out power to Sanctum and reveal the truth about the Primes to the citizens. In retaliation, Russell unleashes a massive amount of Red Sun toxin, causing the citizens to go mad and attack each other with Priya being killed by Delilah's mother in the chaos. The reunited Primes decide to retreat to Eligius IV for the time being, using Raven, Madi and Gaia as hostages while Murphy and Emori choose to remain behind to save their friends.
Credits
Adapted from Wikipedia contributors, List of The 100 episodes. HTML formatting and reference markers removed.