From his private balcony, Professor Bertrand Dillard and his loyal servant discover the unsettling sight of the body of their family friend, Joseph Robin, with an arrow lodged in his chest. However, Dillard quickly deduces that the scene was deliberately staged, as Robin was actually murdered inside the house with a blunt object. Despite the clear evidence of foul play, the identity of the killer remains elusive, with no obvious suspect emerging at first glance.
Dillard lives with his niece, Belle Dillard, who is visibly distressed by the event. Also living in the household is his adopted son, Sigurd 'Erik' Arnesson, a young man returning from college after hearing about the murder. Sigurd is not only Dillard's adopted son but also Belle's boyfriend, and his arrival adds a layer of tension and emotional complexity to the investigation. The nearby houses are occupied by neighbors like the Drukkers—a brother and sister. The sister feels responsible for a previous serious injury inflicted by her brother, which has left him frail and suffering from agoraphobia. She claims she did not see or hear anything related to the murder, despite the possibility that she might have observed the scene from her window. Mr. Drukker admits to having been inside Dillard's house prior to the murder, adding suspicion.
Another neighbor of interest is John Pardee, a passionate chess enthusiast, who appears overly eager to pry into the ongoing investigation. Throughout the case, a mysterious taunting message on typewritten paper, signed by "the Bishop,” surfaces. The note alludes to the nursery rhyme "Cock Robin," which connects to Robin's nickname, and hints at a deeper symbolic game. Interestingly, at that time, a visitor named Sperling (meaning "Sparrow" in German) was present, but he manages to establish an alibi, leaving suspicion elsewhere. The note's typewriter does not match the ones used by Drukker or Arnesson, and Dillard also claims he does not possess a typewriter.
The mystery thickens when Arnesson’s friend, John, is found murdered—shot in the head, an allusion to the "Jack" in the nursery rhyme "Jack and Jill." This cryptic pattern continues when Drukker, sitting in a park late at night, is pushed off a low wall and killed, referencing "Humpty Dumpty," accompanied by a note from "the Bishop." Further tragedy strikes when Bodil Rosing’s character, Mrs. Otto Drukker, is found dead, seemingly from fright, clutching a chess bishop piece, while a valuable notebook detailing Drukker's research work goes missing from their home.
The investigation grows darker as Heath and Markham grow suspicious of Pardee, but their suspicions are confounded when Pardee is found dead—dead with a house of cards and a chess bishop placed atop, symbolizing "This Is the House That Jack Built." As the case unfolds, Dillard expresses doubts about Arnesson’s behavior and mentions the famous Ibsen play "The Pretenders," which Arnesson is fond of, foreshadowing deeper psychological ties and hidden motives.
That night, Belle discovers the typewriter used by "the Bishop" in the attic after saying goodnight to Arnesson. Her discovery is interrupted when she is suddenly attacked from behind. Reflecting on Dillard's comments later, Vance quickly identifies that one of the characters from "The Pretenders"—a bishop named Arnesson—mirrors Sigurd’s character, hinting at his possible involvement. With urgency, Vance rushes back to Dillard's house alongside Markham, Heath, and the police, in a race against time.
They find Arnesson’s window open and him missing, along with Belle. Dillard joins the search, and they break into the locked attic, uncovering the typewriter—but Belle is not there. Instead, she has been tied and gagged in a nearby cupola. Vance and the others then confront Arnesson when he returns unexpectedly. His reaction appears guilty, and Dillard subtly slips a powder from a poison ring into a wine glass, setting the stage for a dramatic revelation.
As tension reaches its peak, Vance exposes Dillard as the true culprit. It turns out he was the murderer, attempting to fake Arnesson’s suicide to cover his own crimes. He had originally planned to kill Robin and falsely accuse Arnesson, but as the investigation progressed, Dillard devised a more intricate scheme to eliminate witnesses and cover his tracks, driven by jealousy and obsession. Dillard had also killed Robin in a staged scene and was trying to frame Arnesson. The guilty doctor’s act of guilt was reinforced when Vance notices Dillard attempting to pour poison into the wine glasses—though Vance had already switched the glasses, preventing the tragedy from occurring.
In the denouement, Arnesson and Belle share a heartfelt embrace, relieved and safe. Vance prevents Heath from recklessly drinking the poisoned wine, exposing Dillard’s treachery once and for all. The case concludes with the revelation that Dillard was ultimately motivated by jealousy and a desire for control, manipulating everyone around him until his scheme unraveled. The story underscores themes of deception, symbolism, and the deadly games played within the confines of family secrets and hidden motives, all wrapped in a suspenseful and intricately plotted mystery.
