In the greengrocer's, Ray calls his late girlfriend Terry. Throughout the rest of the episode and in the titles, she is called Tracey. Michael Kitchen picks up on the mistake, and refers to Tracey as Terry too.
When Foyle and Milner are discussing the case notes, Milner is sitting up in bed. When Foyle leaves, Milner is lying down in the bed as he was the first time he and Foyle spoke.
When the wire is being fixed to the tree it is about neck high for a person standing on the ground. This would be far too low to affect someone riding a horse at their head height, it would impact the horse's neck or head before it could touch the rider.
At 39:26 when Foyle is reading the newspaper, the far left column is a story on the internment of Neville Chamberlain's ashes. The newspaper is dated May12, 1940; however, Chamberlain didn't die until November 9, 1940.
Part of the solution to the murder hinges on whether the moon was shining at the beginning of March, 1940. Foyle claims that it wasn't, but in fact it was a quarter full on March 1st and waxing towards full moon.
The German Woman is thrown violently backwards from her cantering horse, yet the horse is subsequently seen to have its flanks liberally covered with her blood. It is claimed this is not possible. But she was thrown backwards after being decapitated by a wire stretched across the riding path, which would account for the amount of blood found on her horse.
In the end titles, the credit for Focus Puller is spelled incorrectly - Foucs Puller.
The newspaper dates the story as taking place in the spring of 1940 but the flowers Elsie is seen arranging only bloom in late summer/early fall.
The newspaper article Foyle reads about Milner lists him as having a baby son. It also states he played the tin whistle in the hospital choir the night before Foyle first went to see him, which seems unlikely given his mental state. This could be explained as being creative propaganda flourishes by the newspaper.
At 39:30, DCS Foyle is reading the newspaper about Paul Milner. The caption of the photograph in the paper says Sergeant Paul Milner. Later, the doctor at the hospital tries to rouse Milner by calling him Corporal. Clearly, this is an error.
At 39:30, DCS Foyle is reading the newspaper about Paul Milner. The caption of the photograph in the paper says Sergeant Paul Milner. Later, at the hospital, the doctor refers to Milner by saying he was a corporal in Trondheim. Foyle replies that he knew him as a Detective Sergeant. The photograph in the paper shows Milner in military uniform so he should have been captioned as Corporal Paul Milner not Sergeant.