Things take a turn for the gothic in this week's Cork, with an oedipal nightmare that anticipates a whole subgenre of horror films based around dysfunctional families that would blossom at the end of the 60s. We're immediately introduced to the episode's title character (played by Norman Tyrrell, the ever-plotting Sir Gordon Revidge in Cork's ATV stablemate The Plane Makers), as he reads a thunderous pre-breakfast sermon to his four children. The older pair are played by John Porter Davison and Catherine Woodville (Mrs Patrick Macnee), and the younger by Gerald Rowland and a 15 year old Adrienne Poster (later to spell it Posta). An anonymous letter arrives, causing the old man such consternation he nearly collapses.
Sergeant Cork himself barely appears on screen this week, allowing John Barrie a bit of a holiday. He's off to investigate a murder, meaning Bob Marriott's called away, at the insistence of the Home Secretary, from the church robberies he's been investigating to the case of the anonymous missive, the latest in a series received by Enoch Chatterton, MP. Visiting the Chatterton household, Marriott learns that the letters all call in the strongest of terms for draconian measures against prostitutes and their clients. The strange thing about all this is that Chatterton himself is an outspoken proponent of harsher laws against prostitutes - the letter writer just doesn't think he's going far enough.
Thomas and Vera, the elder brother and sister, seem peculiarly stern toward their younger brother Paul, and Marriott is alarmed to discover nasty bruising on the boy's wrist. Paul claims he fell when fetching coal, one of Chatterton's curious rules being that there are no servants in the house after dark: "Sin enough in a man's own bosom, Mr Marriott, without having to share his habitation with workers of iniquity."
Marriott deduces that the letters were written by a child (though the content suggests they were dictated by an adult), and asks Paul to copy part of one out to demonstrate what he means. Of course, what he's really up to is attempting to disprove Paul of writing them (which he does). Marriott suggests the clearly unwell Chatterton should seek medical aid, and is startled to be told that the MP believes hospitals and doctors are only for those who lack faith, and that he is campaigning to prevent the use of chloroform as an anaesthetic as it is "entirely without Biblical authority" and, used in childbirth, "robs God of the cries of women in labour.")
The scene changes from this terrifyingly puritanical household to the diametrically opposed surroundings of a rowdy music hall, where a singer (real life variety veteran Len Lowe) performs in blackface (beyond the pale now, if you'll forgive the pun, but still a popular form of entertainment in the 60s thanks to George Mitchell's minstrels).
And here are two of the people Chatterton and his mystery correspondent are so keen to punish: ageing tart Lil Mayhew (a hugely enjoyable turn from Ann Lancaster) and a prospective client, boozed-up sailor Bert (Derek Smith).
Into this den of iniquity walks Bob, accompanied by a lady friend named Diana (Jill Hyem, later a prolific writer for TV dramas including Tenko, Angels, Howard's Way and The House of Eliott), a scion of the upper classes desperate to slum it among rogues and whores.
The episode's first act comes to a startlingly unexpected conclusion as a doxy is accidentally shoved into Bob's table by the drunkard she's dancing with, and Bob recognises her as none other than the sanctimonious Vera Chatterton.
Bob can hardly believe his eyes, and when he tells Superintendent Rodway what he saw he's told he must be imagining things (Diana, we learn, changed her mind about associating with the underclass after a sailor tried to get rather too friendly with her). News comes of another letter received by Chatterton.
At the Chatterton residence, the increasingly unwell MP rants to his younger daughter Alexandra that his children are drawing away from him. Alexandra suggests that the family need to talk openly about what happened on the night of her mother's death.
Meanwhile, Thomas brutally threatens Paul with "the cellar" if he doesn't behave.
Amid all this strangeness, Bob arrives to speak with the family. He tells Vera he saw a woman just like her, but she claims she was home all evening. Chatterton emerges, having punished Alexandra for breaking his commandment that the late Mrs Chatterton must never be mentioned. As her father collapses once more, Vera claims that the reason mention of her mother is banned is that her father loved her too much to be able to bear reminders of her death. She also lets slip, without being told, that she knows the kind of establishment Bob saw her "double" in. While unwatched, Bob takes a swab of Chatterton's drink. He's then unceremoniously turfed out by Thomas, who claims the family are too concerned for their father's health to care who wrote the letters.
Rodway visits the music hall and catches up with Lil, who it emerges is an old acquaintance of his. She tells him about a girl who made a sharp exit the night before on being spotted by Bob. Rodway puts an undercover man on the mysterious girl's trail.
Bob has the letters examined by a handwriting expert (Desmond Jordan), who confirms they're the work of a left-handed child who has been made to write with their right hand. Bob knows that this is the case with Alexandra Chatterton.
Bob's also discovered that Chatterton's drink contained chloroform: his children are drugging him. Rodway muses on the effects of the "hothouse" Chatterton's brought his children up in: "Never does. Growth's too rich, too freakish".
The pair head back to the Chatterton residence and break into the cellar, which they discover has been made into a bizarre place of worship with the stolen church furniture that Bob was trying to track down.
They end up locked in a cell by the Chatterton children, and watch in horror as Vera leads the drunken Bert into the cellar and lays him upon the altar. He's due to be a sacrifice in the children's twisted version of a church service.
Rodway hits on Alexandra as the most sensible of the children and tries to convince her to set them free. She won't believe anything bad of her siblings, but tells him that their father murdered their mother.
The delirious Chatterton wanders in, and Thomas confronts him over their mother's death. The children believe Chatterton killed his wife because she was having an affair, and ever since have taken this as their template for meting out "divine justice". The appalled Chatterton reveals that in actual fact his wife had a fatal heart attack when he confronted her with her suspicions of her infidelity - which were later proved false. He's banned any mention of her through his inability to cope with the guilt, and realises with horror the extent to which his actions have warped his offspring.
It's now time for Sergeant Cork to enter stage left and save the day, along with the undercover man. They swiftly disarm Thomas and free Marriott and Rodway. "You must tell me about this one of these long winter evenings," Cork tells his superior as he surveys his bizarre surroundings.
The episode ends with Cork replacing the monstrous paternal authority of Chatterton with a gentler kind, as he offers the shaken Paul and Alexandra a bullseye. Never underestimate the power of boiled sweets to make all well.