Clarke and Bellamy go on a mission to find supplies for approaching winter. Some of the 100 accidentally eat nuts with powerfully hallucinogenic properties and lose their grasp on reality. Meanwhile, Octavia seizes the opportunity to help a friend escape, and a terrifying event brings Clarke and Bellamy closer. On the Ark, Commander Shumway secretly assigns one of the 100 to kill one of his own, and the treacherous actions of Diane Sydney are revealed.

Murphy returns to camp claiming to have been held captive and tortured by the Grounders, and Clarke and Bellamy have very different opinions on how to handle his return. Octavia sneaks away to find Lincoln and returns with a serious warning for the 100. Meanwhile, a mysterious virus strikes camp forcing many to be quarantined, and Jasper pulls off a heroic move.