Professor Hibbard (Leonard Mudie) requests detective Nero Wolfe's assistance in tracking down the sender of a few sinister letters, which killed two of Hibbard's acquaintances. Prominent author Paul Chapin (Eduardo Ciannelli), who is a cripple, is pinpointed by Wolfe as the culprit. Wolfe rationally deduces that Chapin is out for payback — decades ago, a prank then-Harvard University scholar Hibbard and a group of chums played on Chapin went awry, causing him to be in his current state. Hibbard shares with Wolfe that his daughter (Irene Hervey) is romantically involved with Chapin's elder brother, Mark (Joseph Allen). With that, he quietly makes a move.