It is May 1940, and Detective Chief Superintendent Christopher Foyle's request for government service is again disallowed and he returns to local police work in Hastings, on the southern coast. Being ostensibly without a licence, he is assigned a driver by the name of Sam Stewart—who, to his surprise, turns out to be a young woman from the Mechanised Transport Corps. Meanwhile, local aliens are being interned, the bombing of England has commenced, and anti-German feelings are running high. Investigating the vicious murder (by near-decapitation) of the local magistrate's wife (who is, in fact, a Sudeten German), Foyle finds corruption taking place (specifically a scheme to keep eligible men from being drafted into military service) and other forms of collusion. Much of the case centres on a local pub, and the case ends with an arrest of a cryptographer at the Admiralty who had developed a relationship with the dead woman. Foyle also often visits Paul Milner, a former police officer whose lower left leg was amputated while serving in the Army, and encourages him to become his assistant.
Set against the backdrop of the Allies' retreat from Dunkirk, the future looks bleak for England - invasion and defeat seem imminent. Paul Milner, while visiting London, meets Guy Spencer, a charismatic fascist sympathizer, politician, and conman, and is invited inside to a meeting. Outside however, a passerby who voices distaste at the meeting is badly beaten. Investigations into a minor sabotage case leads Foyle to a local hotel, The White Feather. At home, Milner is frustrated by his wife who struggles to cope with his amputation, leaving him conflicted between his duties and doubts. Later, Spencer leads a private meeting of the pro-nationalist "Friday Club" at the same hotel at which the hotel manageress is shot dead. Foyle and Milner investigate, and chase up numerous leads including the fisherman boyfriend of the saboteur, a missing letter from the Foreign Office, an army intelligence agent, and a shop-owner whose gun (the murder weapon) was taken from his hotel-room. In the end, the husband is revealed as the murderer, since he longed to be free of his wife's domination.
This episode shows Milner starting back at work as a detective sergeant. He has recently acquired his artificial leg and still requires two crutches to aid him. His wife, Jane, expresses a great dislike for his leg.
Sam tells Foyle that her father is a vicar; he appears in the episode "Eagle Day".
Sam is very pleased to be invited by Foyle to tea at the Crescent and eats more than her share of the food ordered, including the last lemon curd. Her interest and healthy appetite in food appears in other episodes.
Foyle receives a letter from his son Andrew (a voice-over by the uncredited Julian Ovenden), who writes about his training and eating haggis (to hint at his location).
"Woolton" is the name Robert Wolf assumes when staying at the White Feather. However, that is the name used in the credits for the character and his nephew Isaac, even though Isaac never used the pseudonym.
A conscientious objector loses his appeal and is later found dead in his cell. At the house of the judge who sentenced him, an observant young evacuee, struggling to cope with his new surroundings, is killed by a hand-grenade booby-trap in the summerhouse. Foyle's investigation reveals a relationship between the judge's daughter, Susan, and a local worker, Peter. He also becomes suspicious of the actual purpose of the mysterious factory at which Peter works. Later, while guarding the house, Milner is caught in an apparently compromising position with Susan and is asked to leave. Shortly thereafter, the judge is found shot dead inside a room with locked windows, and Foyle's suspicions begin to centre the gun used, and on his wife, who was appalled by her husband's involvement in the young boy's death.
Paul Milner is seen limping and uses one walking stick; it appears he is becoming accustomed to his false leg. However, his wife, Jane, continues to be upset by it. She leaves him, saying she is going to stay with her sister Kate in Wales.
We hear of Foyle's longstanding friendship with Carlo Lucciano, the restaurant owner, which dates back to when Foyle was married.
Foyle mentions that his son Andrew is undergoing pilot training with the RAF in Scotland.
Tony Lucciano asks Sam to be "his girl" and write to him while he is serving. She appears a little reluctant but agrees to do this. There is no reference to Tony after this episode.
The plot centres on an eleven-year-old boy who was evacuated from London. In the months leading up to the war, 1.5 million people were moved: 827,000 children of school age; 524,000 mothers and young children (under 5); 13,000 pregnant women; 7,000 disabled persons; and over 103,000 teachers and other "helpers". However, as a coastal town, Hastings was preparing for invasion, and in June 1940, the setting of this story, vulnerable civilians were evacuated from southern and eastern coastal areas of Britain.
At the end of the episode, it is heard that Italy has declared war on Britain and France. This occurred on 10 June 1940.
With air-raids becoming more common, a local lorry driver is found murdered inside a bombed out house, a gold locket in his hand. Meanwhile, Foyle's son Andrew returns from RAF training and is posted to a local radar station as a test pilot for their systems, but his time there is troubled. Against this, Sam Stewart's father tries to take Sam back home from the apparently dangerous influences of life as a female in uniform. After visiting an art gallery, Foyle wonders whether artworks shipped to Wales by the driver are all that they seem, and is helped when Sam's father identifies a valuable French statue by chance. Andrew's queries and arrest brings the two cases to a head as Foyle senior's investigations reveal the reason - the sexual assault, pregnancy, and suicide of a WAAF, and ensuing cover up (under the guise of Official Secrets Act), and revenge by her father. Eagle day refers to when the Germans attacked radar stations in England (13 Aug 1940); a bomb hit the radar station when father and son walked outside it, but were not injured; the radar was working again in a few hours.
Andrew Foyle is assigned duty flying low altitude missions in a brand-new Supermarine Spitfire, to help calibrate the new British technology of RDF (radar) and finds himself embroiled in the cover-up of a suicide scandal.