Henry and Margaret spend a day at the races with her new client Bob Bishop, who is resisting a take-over bid for his cider brewery. A mysterious man shadows Henry and then the corpse of stable lad Ben Tucker is found in a horse-box. Bob's brother Tony owns the stables, which are failing, and he is very curt with Henry when he comes to investigate. On the night he died Ben had argued with another stable lad Jerry Lawless over female jockey Jude O'Brien but he too is murdered and Bob's daughter Liz, another jockey, is found in his caravan with a bag full of bank-notes.

Liz claims the money is winnings from a bet and Henry releases her but notes that Jerry too has a healthy bank balance and surmises he was trading inside information for cash. Tony apologizes to Henry but tries to push Bob into accepting the take-over and Henry's mystery man proves to be a private eye, since Tony has been fixing races and the Jockey Club have hired him to get proof. Henry believes Tony got Jerry to nobble his horses and killed Ben when he found out. He has the correct motive but the wrong suspect and it's Margaret who literally stumbles on the real killer and has a close call with them. Meanwhile Nicola is annoyed when a spoilt school-friend appears to be making a play for Gary, though she is actually trying to poach him for her restaurant - unsuccessfully.