Porter warns his sons that robberies have recently occurred in the park and asks them to be on the alert for anything suspicious. While playing on the shore, the boys meet a man and woman - the thieves. The two crooks trick the boys into accompanying them to a yawl in the lagoon. Once on board, the thieves knock out the yawl owner, lock the boys in the hold, and begin rifling through the owner’s possessions. Flipper rushes away, finds Porter, and leads him to the yawl. The thieves try to escape but Flipper capsizes their rowboat. Porter then nabs the two.