One bleak Friday evening in January, 1942, Councillor Henry Grayling boards an overcrowded train with £120 in cash – wages to be paid out the next day to the workers of Barrow and Furness Chemistry and Drugs Company. When Councillor Grayling finally finds the only available seat in a third-class carriage, he realises to his annoyance that he will be sharing it with some of his disliked acquaintances: George Ransom with whom he had a quarrel, Charles Evetts who is one of his not-so-trusted employees and Hugh Rolandson whom Grayling suspects of having an affair with his wife. The train journey passes uneventfully in an awkward silence; but later that evening Grayling dies of what looks like mustard gas poisoning - and the suitcase of cash is nowhere to be found.

Inspector Holly has a tough time trying to get to the bottom of the mystery, for the unpopular Councillor had many enemies who would be happy to see him go, and most of them could do with the cash he was carrying. But Inspector Holly is persistent and digs deep into the past of all the suspects for a solution, starting with Grayling's travelling companions.

Somebody at the Door, first published in 1943, is an intricate mystery which, in the process of revealing whodunit, paints an interesting picture of the everyday life during the war.