Fourth grader Scab McNally has a real quandary on his hands. He's convinced after he felt that hard tug on his fishing reel during the fishing expedition with his two best friends and new favorite doggy companion, golden retriever Joe, that he glimpsed some kind of swamp creature. All Scab needs to do is get permission to go back out on Beeson's Lake with another fishing rod (and some special handcrafted dinosaur spying inventions, of course!) and he'll be able to find proof. But before she'll let him back out on the water, Scab's mom insists that he pass the swimming class...
he's being forced to take with his "smart times ten" twin sister Isabelle. That means Scab has to master swimming in the super deep end of the pool, and Scab is NOT ready for that! So, it's back to his top secret lab to diagram some special schemes and plans for the occasion. Will any of them go awry? Well, it wouldn't be any fun if they didn't, would it?