Professor Hibbard (Leonard Mudie) seeks the help of Nero Wolfe (Walter Connolly) to trace the sender of a handful of sinister letters that have killed two of Hibbard's acquaintances. Wolfe quickly narrows the field to Paul Chapin (Eduardo Ciannelli), a celebrated author who is crippled in body, and whose bitterness has shaped his life. Wolfe’s careful deduction points to Chapin as the culprit, driven by a motive rooted in a long memory of personal grievance.
Wolfe explains that Chapin’s motive traces back to a prank decades ago involving Hibbard and a circle of Harvard friends that went wrong, leaving Chapin in his current state. Hibbard adds a personal wrinkle: his daughter, Evelyn Hibbard (Irene Hervey), is romantically involved with Chapin's elder brother, Mark Chapin (Joseph Allen), which complicates loyalties and emotions surrounding the case.
To test the players and their fragile finances, Wolfe arranges for all of Hibbard's surviving Harvard pals to gather at his residence. Most agree to attend, except taxi driver Pitney Scott (Victor Kilian), who stays away, hinting at debts and hidden pressures among the group. Wolfe uses the looming confrontation to observe how the group interacts under scrutiny and to map out potential financial angles that might illuminate the truth.
The tension escalates when Dr. Loring A. "Burt" Burton (Kenneth Hunter) is shot by a hidden assailant during the meeting. Wolfe, noting the line of fire and the source of the blast, argues against Chapin’s guilt and asserts Chapin’s innocence, shifting the focus of suspicion. Soon after, Wolfe and his partner, Archie Goodwin (Lionel Stander), are captured by Mark Chapin, who resents being double-checked and hates Wolfe for an earlier accusation.
The pair manage a daring escape, and Inspector Cramer (Edward McNamara) promptly arrests Mark for kidnapping. With the齟turning of events, Wolfe returns to the core puzzle: Chapin did send those letters, but only to frighten, not to kill. The real killer emerges from the shadows as Ferdinand E. Bowen (Walter Kingsford), a banker and one of Hibbard's friends, who reveals himself through a background-check trail. Bowen had fed Wolfe the debt details and used Chapin’s letters as a decoy to mask a more calculated crime: Bowen had stolen the money behind the men’s debts and orchestrated the ruse to cover his tracks.
In the end, Wolfe’s methodical reasoning clears Chapin of murder and exposes Bowen as the true perpetrator, tying together the threads of debt, deception, and a carefully staged fear. The case resolves with a reminder of Wolfe’s cool, rational approach: motive, opportunity, and opportunity taken are all weighed against each other until the truth emerges from the carefully structured web of lies.
