Gordon sets down a summer challenge to his son Jack: can he complete a gruelling 1.1-mile open water swim across the Cornish Camel estuary in under 40 minutes? Jack accepts. It's a tough, dangerous swim, battling against strong tidal currents, so Gordon and Tilly are taking no chances with Jack's safety. They are sailing in the back-up boat, skippered by Ian from the RNLI. If Jack succeeds Tilly is going to cook him a special Cornish lunch to celebrate - Stargazy pie, lovely lemony broccoli and a Cornish ice cream cake made with cream straight from the local cows. But if he fails and has to be rescued, she is going to call it loser's lunch!