A chess prodigy is poisoned during a club tournament, and the police arrest the member who served the victim hot chocolate. Wolfe is hired to exonerate the suspect, but finds that no one else has either an adequate motive or the requisite opportunity.
Gambit employs three distinctive plot elements found in other Wolfe stories. The means by which poison is administered is very similar to the means used in "Cordially Invited to Meet Death." A tape recording is made in an Italian restaurant, one which also appears in "Poison à la Carte"; and the part that a gambit plays in a murder echoes "Method Three for Murder."
Sally Blount's father, Matthew Blount, has been arrested for the murder of Paul Jerin, a chess master. Blount had arranged for Jerin to play twelve simultaneous games of blindfold chess at his club. Well into the contest, Jerin complains of physical discomfort and cannot continue. Shortly thereafter, Jerin dies of what tests show to be arsenic poisoning.
During the contest, Jerin had been sitting by himself in a small library off the chess club's main game room. He had nothing to eat or drink except a pot of hot chocolate, brought to him by Blount. After Jerin fell ill, he was diagnosed by a doctor who was playing in the contest; the doctor called for an ambulance but Jerin died at a hospital.
Not only had Blount brought the hot chocolate to Jerin, he had washed out the pot and the cup after Jerin complained that he didn't feel well. Blount is charged with murder.
The only people to enter the library where Jerin sat, other than Blount, were four messengers, who relayed the moves between the main game room and the library. The messengers apparently had no good opportunity to put arsenic in Jerin's chocolate.
Dan Kalmus is Blount's corporate lawyer, and represents Blount after he has been jailed without bail. Blount's daughter Sally is convinced, however, that Kalmus is in love with Blount's wife Anna, and that he won't be inclined to give Blount his best legal efforts. Furthermore, Blount's specialty is business law, not criminal law, and he might not have the needed background.
But Sally is certain that her father is innocent, so she hires a reluctant Wolfe to investigate on her father's behalf. Neither Wolfe nor Archie seems to have his heart in the case because the circumstances point so clearly at Blount. And Wolfe learns from the police that their own inquiries discovered no connection between the messengers and Jerin, whereas Blount was unhappy that Jerin had been seeing Sally.
Because none of the messengers could have a motive to kill Jerin, and because he has assumed that Sally is correct that her father didn't, Wolfe conjectures that Jerin was poisoned not because the murderer had it in for Jerin, but to get at Blount, whose apparent motive would surely get him arrested. Wolfe's hypothesis, then, is that Jerin was a pawn, sacrificed in a gambit to get rid of Blount.
Wolfe speaks with each of the messengers as the best alternative suspects, to try to determine which of them might have wanted Blount, not Jerin, out of the way. Each of the four has a possible motive: Sally thinks Kalmus is in love with her mother, Farrow would like to take over Blount's firm, Yerkes wants Blount's vote in a in a board election but won't get it, and Hausman resents Blount for going easy on him in chess games but winning anyway.
Wolfe learns that there is, in Blount's words, "a certain fact" known only to Blount and to Kalmus that will demonstrate his innocence. The fact turns out to be that Blount really did put something in Jerin's chocolate, but it was sedative in effect, not poisonous. This puts a very different face on things, and as a result Wolfe and Archie, independently, are able to infer both the murderer's identity and how the arsenic got into Jerin.
The series of black-and-white telemovies stars Tino Buazzelli (Nero Wolfe), Paolo Ferrari (Archie Goodwin), Pupo De Luca (Fritz Brenner), Renzo Palmer (Inspector Cramer), Roberto Pistone (Saul Panzer), Mario Righetti (Orrie Cather) and Gianfranco Varetto (Fred Durkin). Other members of the cast of Sfida al cioccolato include Micaela Esdra (Sally Blount), Mario Maranzana (Matthew Blount), Silvia Monelli (Anna Blount), Paolo Carlini (Daniel Kalmus), Giampiero Albertini (Ernst Hausman), Renato Campese (Morton Farrow), Renato Turi (Charles Yerkes) and Mario Laurentino (Piotti).