A tropical island vacation with the Turtle family and Bear turns into an underwater exploration adventure! Franklin and Bear are thrilled when Mr. Turtle surprises the boys with a tour of their favorite submarine rescue sub, the AquaRescue 3000, only to be disappointed when they arrive to find that the tour has been canceled. Just as they are about to turn back a spirited young river otter Olive invites them to tour her sub, an old wooden steam punk sub named the Seaplunker, captained by a wise old sea turtle, Cap’n Delmar.