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 Aqua-Rescue 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.