John Murphy returns to the group. He was captured by the Grounders who tortured him for information about the group. Soon, a deadly virus spreads thanks to the presence of Murphy, who was used by the grounders to spread weakness among the group in preparation for an attack. Raven builds a bomb to stop the grounders from crossing the bridge featured in the previous episode. Bellamy gives Jasper the task of detonating the bomb. The bomb is successful just as the raiding party reaches the bridge. Murphy smothers a member of the group that originally tied the rope around his neck some time prior.