Since Jamie Oliver's push for healthy school meals, sweets have been banned at Elmsbury High. But someone is running an unofficial tuck shop selling crisps and chocolate - and Nathan is given the job of finding out who is behind it.

It's the end of term and Nathan is due to be assessed by headmaster Mr Byron. His future hangs in the balance. So when Josh messes up, and it looks like Nathan's career as a teacher is over, it's down to the rest of the 4 O'Clock Club to save his skin.