Grantchester opens with the weekly eucharist, Will and Leonard presiding. But somewhere in dark alleys, there's a man on the run, begging someone to take his money. As Vic and Marie round up his gang after church, Mrs. Butler thanks them (and Will) for taking care of her son.
As Marie quietly thanks Will for being a friend to Vic, down at the station, the beaten gentleman in question, Walter Burrows (Rupert Holliday-Evans), has come to report his mugging. However, he refuses to give any details, suggesting he's only doing it to appease the wife sitting next to him.
Ellie: Will Davenport, will you marry me?
Ellie: See? Now we're even.
Will pops by to round up Geordie, and they head to Vic's for Sunday evening boxing starring Lucas and Matthew. Jack's there too, plotting with Leonard to win Mrs. C back. Ellie's also on hand, though Will is steadfastly ignoring her. Vic gives an inspiring speech ahead of the match, thanking Will for his help in training, and Geordie's more begrudging support for not arresting any of the boys. Will plays coach ringside, but the fight descends into a one-sided blowout, as Matthew seems to lose his will to compete. Afterward, everyone meets up at the pub, but the combatants don't turn up. Vic and Will head back to get them, only to find the door locked, and a sign "Don't Come In, Call For Police."
Will breaks down the door to find both Matthew and Lucas unresponsive in the ring, an empty bottle of benzedrine between them, and signs both have ODed. As they lay in the hospital, Will tries to insist it couldn't be an attempt at double suicide. But Geordie's got a darker theory. He finds a receipt for personal ads in Lucas' locker advertising himself as a "young male companion" for "friendly gents," that also has a story in it of a husband who killed his wife and faked it to look like a near-double suicide to avoid charges. Despite Will's behavior, Ellie rounds up the only response to Lucas' advert, which came through the paper's mailbox system.
The envelopes' franking leads to the local bank, which has an employees-only machine. Luckily, Geordie recognizes an employee: Burrows, the man trying to avoid reporting his own mugging. Burrows pretends he wasn't looking for sex, but admits he did respond to the ad. Upon arrival, he realized Matthew was following them, and the two robbed him. Back at the hospital, Matthew wakes from his coma, telling Geordie this was an attempted suicide, and they left a note. When Geordie asks Vic if he knew about Lucas and Matthew's activities, Vic says he knew they were up to something and told them after the match they were done at the gym.
Will is shocked to learn Vic was planning to toss the two out and horrified Geordie thinks Matthew staged his suicide as cover to murder Lucas. He goes to see Burrows, who confesses he and Lucas went back to the gym. But he insists Lucas was willing until Matthew showed up, ranting: "He makes us think this is normal." Will heads to the gym thinking to find evidence but instead sees Vic giving one of the boys a backrub. Remembering how Matthew freaked out at being touched, Will looks at Vic in dawning horror. But before he can say anything, Marie arrives with the news Lucas is dead.
Geordie once again pushes Matthew-as-murderer now there's a dead body. But Will asks him to get Vic out of the room and let him talk to Matthew. It takes a bit, but Matthew finally opens up, describing how Vic grooms the boys, gets them drunk and horny and gaslights them into thinking they want it. Matthew's response was to act out, get arrested again, trying to escape. Lucas figured to at least make money for it if adults were going to abuse him anyway. Vic seems shocked by the accusations when Geordie takes him for questioning, admitting he bought the boys porn mags, but he bought them lots of stuff. When asked about Matthew's confession, he throws the kid under the bus, calling him a criminal and a liar.
Will storms out only to find Mrs. Butler taking Matthew away, calling him a pervert. Matthew freaks out and punches Will, and gets locked up. With no evidence to hold him, Vic walks free. Geordie takes Will out for a drink and tells Will about having Diana committed. He sighs how well Cathy hid it. It was, after all, what she'd grown used to. Will looks up and realizes that Cathy wasn't the only one used to keeping secrets. Matthew said he'd tried to tell someone, and Will realizes it was Marie. Confronted, Marie denies she went back to the gym, found the boys, or stole the note. But as Will leaves, she hands him the missing suicide note.
Leonard's plan of action to bring Mrs. C and Jack around is to have Jack come in and do all her daily chores at the vicarage, leaving the two of them the day to "work out their differences" while Leonard mediates. Unfortunately, Leonard isn't a great therapist, allowing Jack to dominate the conversation He accuses Sylvia of never caring where his money came from when they first married, and she found herself a rich woman. But he does say he'll go if she wants and leave her everything, before storming out.
Having failed at regular therapy, Leonard loses it and goes for tough love. He rounds Jack back up and lays down the law that he doesn't want to see either of them again until they've stopped being stubborn mules and find a solution. He storms out with Dickens in tow. It works. Jack admits he can't change his past, but he's written to Tariq and has offered to support his family financially. It will mean no more lavish spending, but Mrs. C is ok with that, she just wants to be comfortable again.
As they make up, Leonard and Daniel walk Dickens, and Leonard pulls out the letter his father sent in response to the one he sent last week. Daniel reads it and tells Leonard he is strong enough to face his fears and see his father once more. Meanwhile, with Will confronting her with Matthew's words, Marie finds her inner strength and steps forward to give a statement. But it's all too much for Will, whose final speech from the pulpit this week is heartbreaking. Everywhere he turns, the father figures betray him.