A smudge on a prefect badge leads Moon and his detecting sidekick to expose criminal activity in an unlikely quarter.
It is a proud day for Moon's sister Hazel as she is sworn in as a junior prefect, but more importantly, she now has open access to head boy and school heart-throb Nigel Godfrey.
For Moon, a new investigation beckons as a mysterious note appears on his locker. On it is written 'Stop Them', and a prefect's badge is attached. Closer examination reveals clues which suggest some illicit activity linked to Pupil Enterprise Week, but what could it be? Moon is on the case, and squeaky-clean Nigel soon has the finger of suspicion pointed at him over unwelcome secrets from his past.
Meanwhile, Red's brother Herod is doing a surprisingly roaring trade on his cake stall; that is, until April discovers his secret ingredient.