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.

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.

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.