Josh and Danny are on a day out with the local nature group, but when they accidentally eat a chocolate muffin laced with S.W.I.T.C.H formula, they experience the real dangers of pond life first hand. Soon the boys are beetling about in a pond, breathing underwater, and creating the most almighty stench to scare off predators. But life as a pongy pond beetle is the least of their problems-there's a mysterious stranger hanging around-and he's out to get them.

Will Josh and Danny find out who the stranger is before it's too late? And can they help Petty Potts in her mission to recover all of the REPTOSWITCH cubes so she can turn them into even more exciting beasties? Petty Potts's diary entry: I do hope Josh and Danny will come round tomorrow-they have to understand the DANGER we're all in! And of course, I really need their help. I'm sure I will manage to talk them around. After all, they both can't wait to try out being a giant python or an alligator or a monitor lizard.