Saul Arkwright walks his dog close to Lord Ashfordly's estate when the dog is shot by one of Lord Ashfordly's guests Oliver Langley. Since Langley just drives off nearly hitting Arkwright in the process the latter see no other alternative than to make a complaint to the police. When the police do not do enough in his opinion Arkwright takes matters in his own hand. Vernon Scripps has had a new "bright" idea. He has bought a surplus U.S. Army half-track tank to drive tourists around the countryside. But since he has a boil in a very private place David has to drive the half-track for him. David only flattens half the village trying to get the hang of it.

Masked robbers stop a train just outside Aidensfield and get away with several mail bags containing cash and securities. The train driver Brown tries to stop them, but is gunned down and killed. The case is assigned to DI Ludlow, who is none too pleased to see PC Mason again. Especially since Mason has a lot of suggestions on how to catch the robbers and Ludlow has already formed his opinion on who is behind it. Mason on the other hand only wants the robbers to be caught because Brown leaves a wife and two small children, and wins DS Dawson over on his side. Aunt Peggy gets a letter from a solicitor telling her she is the heir of a distant relative and she is convinced there is a fortune in it for her. Even when she learns that her inheritance is a race horse in stead of money, because she reckons she will earn a fortune in prize money - that is at least until she sees the animal.