The Wishing Chair Again. Chapter 8 - The Slipperies Play a Trick

Peter and Mollie wait for Binky and try to make sure they aren't tricked by the Slipperies. They want them to go away so Peter tricks them into going and they both feel pleased they managed to avoid being tricked. But when Binky comes back they find out they have been! What was the trick and how do they fix it?