On the run from a terrifying predator, the boys glimpse an unbelievable sight. Irene leads her team deeper into the island. Mike makes a confession.

Annie and Dog stage a subterranean rescue operation. Irene gets better acquainted with the island's wildlife. Cap explains an intriguing theory.

A risky plan pays off, leading to a reunion — and new revelations. Stuck in a precarious situation, Charlie and Dog form an uneasy alliance.