When Petty Potts leaves town, she puts Danny and Josh in charge of some of her special S.W.I.T.C.H. spray. But leave it up to the nutty scientist to put S.W.I.T.C.H. spray in a bottle identical to their sister Jenny's hairspray. When Danny and Josh's big, annoying sister transforms into a little, annoying crane fly, it's up to the two of them to keep Jenny from being eaten alive. But that would be much easier to do if their own legs would stop falling off!