As Steve prepares to go off to the camp at Possum Lake with the family and participate in the many contests with his dad, Snot is disappointed that he'll be left behind. However, when the family arrives, Steve and Stan find out that Snot has hooked up with Tuttle to be his stand-in dad for camp games. Although they are awkward with each other at first, they manage to surpass Steve and Stan in every event. Determined to break them up before a big boat race, Steve pretends to be an even better surrogate son online. This triggers a fight between Tuttle and Snot that results in the desired break up. But when Stan refuses to participate with Steve after the dirty tricks, the latter decides to hook up with Tuttle himself.
Meanwhile, Klaus finds himself swallowed by a legendary giant fish named Old Ulysses. Roger is bored at camp until he decides to lead a group of bicyclists, even though he can't ride a bicycle. His ruse is ruined when the real bicyclist group leader arrives, having mistaken Roger for yet another mythological being at the lake after he was attacked by Roger. Hayley and Francine set out to get the darkest tan possible.
With Snot out of the race and Stan struggling to sail his ship alone, Steve starts to feel regretful that he may have hurt two people close to him. But things go crazy when Old Ulysses decides to attack the regatta, wrecking boats and swallowing Tuttle in the process after being accidentally knocked overboard by Steve in his attempt to save Stan. When Stan is knocked out cold from one of the fish's attacks, Steve is able to revive him with Tuttle's stash of energy drinks. Together, they fashion a hook out of an anchor and manage to land Old Ulysses, freeing Klaus and Tuttle as well, as Hayley and Francine imagine themselves turned into star beings, although this is only a hallucination brought on by too much sun. As Steve admits that he's so competitive because he's afraid his dad wouldn't want to come to the camp if he wasn't, Stan reveals that he comes just to get away from work. Making up with Snot, he suggests that maybe he could come with them on a future camping trip although Stan gives a flat "no" on this. With Old Ulysses caught, a new legend arises about the mysterious land beast.