Clarke, Bellamy, Octavia and Jasper hit a tragic roadblock. Meanwhile, Raven and Monty make an important discovery.
Octavia fights in the final battle for the survival of her people, but not everyone is willing to play fair.
Clarke and Roan must work together in hostile territory so they can deliver a valuable asset to Abby and her team.
At the outer reaches of the world, a team of scientists discover a new highly intelligent species, but its existence may endanger more than their research.