A mysterious castaway appears while Charlie, Mike and their dads search the ocean for mythical creatures, throwing all their plans into chaos.

As they adjust to wild new surroundings, Mike and Charlie realize that getting to shore was the easy part. Cap encounters another explorer.

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.

Mike's injury catches up with him, while Annie and Irene unpack their complicated histories. Dog and Charlie's journey across the island continues.

Years in the past, Kong roams the island with a beloved human friend. But when his temper gets the better of him, the consequences could be dire.

Charlie proposes a daring plan to defeat the sea monster and save Mike's life. But it will take all his courage — and Kong's strength — to pull it off.