So we've got some people from a clan whose name I forgot (and could not pronounce even if I remembered it) challenging Roan for leadership. In order to take over, he needs to win in a battle. Ordinarily, this would not be a problem, but Roan is still healing from being shot. Echo begs him to let her battle in his place, but he turns her down, saying that if he doesn't fight for himself, the clans will all fail to follow his lead, even if she wins.
Kane and Octavia try to talk the clan's ambassador out of the challenge, but he will not be moved. So, Octavia goes to later and kills him (making it look like he died of natural causes). So, the fight will go on, but the ambassador to the clan is dead.
Back in Arkadia, they come up with a plan to reseal the ship and live there for the next five years while they wait out the radiation. However, it will only hold 500 people, which means they can only save Skaikru, and not everyone else, as Clarke and Bellamy promised. However, they need a hydro-generator to make water, so they head over to Farm Station (which is currently occupied by Ice Nation) to get theirs. However, when they get there, they realize Ice Nation is holding members of Skaikru as slaves and decide to use the generator as a bomb to help them escape.
They end up free and back at Arkadia, but now we have no way to get water. Which means, our group of 500 may end up at around 100 instead.
Oh, and Kane and Abby end up getting together for real! I can totally get behind this.