Facing an unknown enemy, Wells attempts to keep the group together. Clarke strikes out for Mount Weather, in search of other colonists, while Bellamy is determined to rescue his sister, no matter the cost. And back on the ship, Glass faces an unthinkable choice between the love of her life and life itself. In this pulse-pounding sequel to The 100, secrets are revealed, beliefs are challenged, and relationships are tested. And the hundred will struggle to survive the only way they can--together.