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

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.

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

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.