Raven gets communications up between the drop ship and the Ark.
Abby assists Clarke through a desperate procedure in order to save Finn's life.
Bellamy brings the Grounder to the drop ship to question him. When they realize Finn's been poisoned, they torture the Grounder for the cure. The Grounder doesn't break until Octavia poisons herself, then he reveals the antidote to save her and Finn.
Abby is saved by the Council from being floated for her crimes because she's essential personnel, but she's removed from the Council. She's replaced by Diana, the former Chancellor, who as her own agenda.
Jaha calms the outrage over the culling by revealing his son died and that those who sacrificed themselves gave those left the chance to make it to Earth.
Project Exodus is the plan to get people to Earth. They weren't expecting to have to use it for years and they don't have enough resources to make drop ships for everyone to go.