Notorious burglar Albert Hallows – aka ‘The Prof’ – has escaped from Armley Jail and he has a score to settle with Aidensfield police. When Hallows is disturbed in a barn by two young boys, Mickey and Bill Gracey, he tells them he’s a spy, on a secret mission to find some treasure. Hallows enlists their help – but says they must sign the ‘Official Secrets Act’ first.

Hallows uses the Gracey brothers to help him break into ‘enemy’ Mrs Halloran’s cottage and steal something as a reward.
Later, the boys agree to obtain the keys for Davenport Manor, where their mum does the cleaning. But when Mickey falls ill, Carol visits and spots a piece of wax fruit in his bedroom, which was reported stolen from Mrs Halloran’s cottage.

Back at the station, DS Dawson and Miller question Bill, who refuses to reveal anything about what Hallows is up to, fearing he’ll be hanged if he breaks the ‘Official Secrets Act’. Meanwhile, Hallows escapes in Mrs Gracey’s car and heads for Davenport Manor. Will Mickey reveal all before Hallows commits another crime?

Also, Dawn gives Pc Younger ballroom dancing lessons so that he can accompany Joyce Jowett to a charity dinner dance. Carol invites Joe to the ball, and is dejected when he doesn’t show, still busy chasing Hallows. After their dance tutorials, Younger thinks he stands a chance with Dawn – but he’s left heartbroken when he sees her dancing with another man.

*Guest starring George Cole*