Screwtop Spudswap

Dennis is desperate to prevent Pieface from failing Mrs Creecher's maths test! He persuades the gang to use Professor Von Screwtop's mind-swapping device. But in a disastrous turn of events, Screwtop is on the loose with the brain of Paul the potato and Pieface is left with a potato with the brain of Screwtop to help get him through the test!