It is Katie's christening, and everyone is celebrating at Nicks house afterwards, when an old girlfriend of his, Gill, from the Met turns up for a visit. Nick and Gill are asked to go undercover to investigate the criminal activities of the owner of a well known gambling club. Blaketon thinks that Mr Armstrong is going to cheat in an up coming racing event by tampering with the favourite horse, ‘Fab Four'. The police are on to him, and he soon notices he's being watched so he kidnaps Gill and hides her in a horse box. Nick and Phil come to the rescue.

Claude's nephew comes to visit but he brings his latest business partner who is American along with him. They ask Claude if they can use his place for storage. There are a few burglaries in the area including Ashfordly hall. Walter Gillis is trying to put Bill Ruane in the frame because he wants a chance to buy his stables. But it turns out that it was Walter himself who robbed Ashfordly hall, and it was the American who had done the two other burglaries. Claude is upset to find that the stolen goods had been hidden on his property. Nick asks Jo to dinner but is called out and Jo offers to baby-sit. Eileen comes home to find her curled up asleep on the sofa with Katie.

An old flame of Eileen's turns up. He is a French man named Antonin, who urges Eileen to marry him. She declines because of her commitment to Katie. Nick goes undercover as a harbour worker to catch an escapee prisoner. Phil goes missing during the operation and is found trapped on one of the boats. Claude is buying fish under false means, Nick notices what's going on and advises him to stay away from Whitby - which is where the investigation is taking place.

Alf has to deal with a group of travellers who have a grudge against him. Alf is determined to catch them at whatever crime they're about to commit. He feels guilty for not convicting them of a crime they committed in the past during which one of his old colleagues was crippled. Alf spends time observing them and making notes, but unfortunately he is spotted and they take him and tie him up in a horse box. It is a race horse that they intend to steal, but during the process Alf makes his escape and drives off in the horse box. They follow him but road blocks have been set up and the thieves are caught. Greengrass lets some guides camp on his land but it proves more hassle than he bargained for.