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.
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.