Early on in the film, when Reverend William Thorne (Robert Donat) and his wife in the vicarage, they are discussing a book being returned to them. It's a copy of The 39 Steps (by John Buchan). Robert Donat (Rev Thorne) played Hannay in Alfred Hitchcock's 1935 film of The 39 Steps.

Opening credits: The events and characters portrayed in this film are fictitious.