Continuity mistake: In episode 2-4 "The Funk Hole " which takes place in the fall of 1940, Andrew states to Sam that his mother died when he was eight years old. In this episode (Feb to June 1941), Foyle is looking at his wife's grave; it shows his mother died in 1932, which would have meant Andrew was born in 1924, and only 16 in 1940, far too young to be a Spitfire pilot. Also, his commanding officer states "the younger pilots look up to you, Andrew", before one of the "younger" pilots (age 19) is badly burned in a crash in Andrew's plane.
Factual error: The naval captain in this episode has a military mustache as prescribed by army regulations. The Royal Navy regulations, however, prohibited separate mustaches and beards - if facial hair was worn, a "full set" of beard and mustache with the beard joined to the mustache was mandatory, and that to be grown to the commanding officer's satisfaction within six weeks.
Factual error: When Sam reads the newspaper, one article claims that 254 people were killed in a Paris air raid. This episode takes place in February 1941, when Paris was already occupied by the Germans, and England did not bomb Paris. Oddly enough, this same article appears in a previous episode.
Factual error: In the scene when Foyle meets the Home Guard colonel, Letwin, the colonel, has his Sam Browne belt slung over his left shoulder which is totally wrong, especially for an officer risen to field rank. Apart from being intended to provide support for the officer's sword (even if not worn and even if his service revolver is likely to induce sagging), the belt slung over the left shoulder will obscure medal ribbons. Horror of horrors.
Factual error: The episode takes place in 1946. Numerous scenes are shown in which the public buildings are clean. In 1946 they were soot streaked and grimy black and white from generations of coal fires and pollution. In addition one street scene has a street sign on a pole with a modern graphical notice on it rather than a worded notice of the time. Also, in the same scene the street name plate has a rather updated type face.
Continuity mistake: In the final scene when Miss Pierce in a car asks Foyle to get in, she looks rather more presentable initially with her hair in curls partly framing her face, with noticeable red lipstick and possibly make up. When Foyle gets in the car and takes up the conversation, the hairstyle reverts to her usual dowdy plain style off the face and the lips are natural.
Character mistake: At the very end of the episode, a chess board is set up wrong, the initial position must have the white queen on the white square (d1) and the black queen on the black (in this case red) square (d8). They set up all the other pieces correctly except the kings and queens should be reversed.