Silver has been marooned on an uncharted planet. Jim and co. set out to rescue him, but there's more to this world than they thought. Now, they must find their ticket home while battling a ruthless pirate and sea witch, with the help of a strange mermaid.

Sequel to His Treasure. Adjusting to his new life under the sea, Jim Hawkins is struck by tragedy when Ariel and her sister, Attina, are kidnapped. In order to get his beloved mermaid back, Jim must enlist the help of old and new friends...