Synopsis of Champagne for One
Archie Goodwin receives a phone call from an acquaintance, Austin “Dinky” Byne, asking for a favour. Byne routinely acts as a chaperone for an annual dinner hosted by his aunt, Louise Grantham Robilotti. The dinner is given in honour of four young unwed mothers living at Grantham House, a charity supported by her late husband. Byne claims to have a cold and is unable to attend. Although skeptical, Archie agrees to stand in for him, despite Mrs. Robilotti being a former client of Nero Wolfe’s who bears him a personal dislike.
During the dinner, Archie learns from one of the unwed mothers that another, Faith Usher, has a bottle of cyanide in her purse. Faith has been suffering from depression, and her friend fears that she might attempt suicide. Archie promises to watch over her, but towards the end of the evening Faith collapses and dies from cyanide poisoning after drinking a glass of champagne.
Alone of the guests, Archie maintains that Faith Usher did not commit suicide. He claims that he observed her constantly throughout the evening and that she never had an opportunity to pour the cyanide from her bottle into her glass. Although the authorities and the other guests pressure Archie into changing his story. Nero Wolfe believes him and decides to settle the matter by solving the case himself.
He is given further incentive to do so when Edwin Laidlaw, another of the chaperones, approaches him to hire his services; Laidlaw is the father of Faith Usher’s child after a brief affair they had the previous year and, ashamed of his conduct, is desperate that his secret is not revealed.
Although Wolfe’s investigation begins unpromisingly, he becomes convinced that his suspicions are correct when the police receive an anonymous tip revealing Laidlaw’s secret.
Synopsis taken from: https://en.wikipedia.org/wiki/Champagne_for_One