Dean goes missing on Monster Beach and Jan must find her brother with the help of Amphibia, who figures out he has been abducted by Captain Kelp with a penchant for boardgames and a hunger for souls. The Captain proposes a deal. They play to win, and if they lose, they must work as his crew for eternity. But outsmarting a Captain Kelp in an undersea lair, playing a game where he wrote the rules shouldn't be that hard... right?