This summary is in no way intended as a substitute for viewing this fabulous episode.
Foyle and Milner visit the Messingers, who are distraught to learn of their son's death. Foyle asks about the watch, but they say he didn't possess one. The engraved date is that of his 21st birthday. The letter is confirmed as being in his handwriting, but they know nothing of Marion Greenwood. Foyle is told that they last saw their son two weeks ago when he came for lunch. He was in an excitable mood. Sir Giles won't tell Foyle what work his son did, as it was classified, but says he will report the death to William's superiors. He remarks that his son's death obviously had nothing to do with his work and asks that the policemen now leave. Foyle leaves, but before doing so says that the circumstances of William's death are not so clear to the police, so he may have more questions later.
As they walk to the car, Milner comments to Foyle that the Messingers raised more questions than they answered. They didn't know his girlfriend and if they didn't give him a watch for his 21st, who did? Lady Anne Messinger catches up with Foyle says there is something he should know. She thought that, when William came to the house, he was more afraid than excited and he had a friend with him called Jan Komorovski, whom she knows he was working with in Hill House in Leavenham. Sir Giles calls from the garden and his wife retreats.
When Foyle has gone, Anne tells her husband that she told him nothing. Sir Giles is remorseful about his relationship with his son, saying that his failure to be a good father had driven William to do what he did.
Foyle takes his brother-in-law to lunch. Howard tells him that normally the Navy would fill the post he mentioned with one of their own, but men, good men, are in short supply. "They need a first-class mind and it might as well be yours."
Foyle asks about Giles Messinger. Howard says he is very senior and influential in the SIS, the Secret Intelligence Service. He ran Section D but they took half his men away from him and he has been very angry about it ever since. Howard warns his brother-in-law not to get on the wrong side of him unless he wants to spend the rest of his career back on the beat.
In the station, Sam overhears Foyle mention Leavenham to Milner and says that if he's referring to the village in Hampshire, then her uncle is the vicar there. Foyle tells her that they are going there. He instructs his sergeant to revisit Mrs Thorndyke to find out how long she has really been in Hastings, and also where her husband went to school, because she seemed reluctant to tell them. Milner comments on her identifying the pocket watch without really looking at it. Foyle instructs him to have another word with Marion and to keep looking for Fenner. As he and Sam leave, he tells Milner that they will be gone for a day or two.
Lt Col Wintringham visits the Messingers to commiserate over their son's death. He tells them that the week before, William had been disappointed to be pulled out of an operation and had been given a few days leave to get over it. Sir Giles says that a policeman by the name of Foyle implied that there were loose ends concerning William's death and he appears to be conducting a criminal investigation. Wintringham reports that Foyle is a troublemaker who has a reputation for "extending his authority into places where it has no right to be." Lady Anne looks pointedly at the colonel and remarks that the DCS seemed to her to be a very honest man.
Sir Giles tells Wintringham that if Churchill had listened to him the SOE would never have stood a chance of being formed and he is still profoundly disappointed that his son chose to defy him and join the organisation. "If I find that you were in any way responsible for his death, I will destroy you."
In an underground chamber, two men in German uniform drag Jan Komorowski into an interrogation room and try to force information from him by repeatedly holding his head under water. A short time later, the interrogators emerge from the chamber into the hallway of a large country house. As they light cigarettes, one says to the other in impeccable English, "I think that went rather well, don't you?"
On the way to Leavenham, Foyle remarks to Sam that Milner is working long hours and is very quiet. He wonders if anything is wrong, but Sam says she knows nothing she can repeat. Her boss indicates understanding and doesn't press further.
When the pair arrive at the Revd Aubrey Stewart's vicarage, the vicar tells Foyle he's welcome to stay as there is plenty of room. Asked about Hill House, he says it was requisitioned by the military but no one knows why and he has become uneasy about the people there. One chap always seems to be loitering around, and there have been incidents.
Stewart hands a glass of his home-made greengage wine to each of his visitors as he tells how he was called out one night to see a parishioner whom the person on the phone said was dying. When he says he cycled six and a half miles to get there, Sam queries it and her uncle explains that petrol coupons aren't issued for that sort of thing. He continues by saying the callout was a hoax, his parishioner was fine, then pauses to ask, "How's the wine?"
Foyle struggles to find a way to describe the drink. "It's, em…" He flashes a look at Sam, who immediately comes to his rescue.
The vicar chuckles and agrees. Foyle asks what else has happened and he says that the next day it was discovered that someone had smashed a flower vase from one of the graves in the churchyard. The grave was only two days old and was that of Ted Harper, a young local man who had died after falling off a roof. Stewart has a feeling that these things are connected with Hill House.
On the drive to Hill House, Sam expresses puzzlement as to what makes her boss think that the suicide of a man over a girl in Hastings has anything to do with what's going on there. Foyle says he doesn't know yet, that's why they've come, he's just curious.
The Army guard at the gate obstructs Foyle's entry to the grounds and rings the house for instructions. Hilda is in Wintringham's office when he receives the call. She is alarmed and says that she knew he'd find them. Wintringham is puzzled as to how he did it. Hilda says she told him Foyle is clever. The colonel suggests that they ask him. Hilda is further alarmed. "You're not going to let him in?"
"You know what they say about keeping your friends close and your enemies closer."
"Yes, well I'm not sure he's either."
Wintringham says that Foyle can be controlled in Hill House, official secrets and all that, but outside, he's a loose canon. Hilda is concerned that the visit might be reported to Sir Giles by the spy, but Wintringham then suggests that Foyle might be of use in uncovering the agent. Hilda strongly warns against, but the colonel instructs the guard to admit the DCS.