The novel is narrated by Bertie Wooster, a good-natured but hapless wealthy bachelor, and centers on his relationship with his brilliant valet, Jeeves.
Bertie returns to his London flat after two months in Cannes with his Aunt Dahlia and cousin Angela. Jeeves informs him that Gussie Fink-Nottle, a reclusive old school friend who studies newts in rural Lincolnshire, has been calling repeatedly. Gussie has fallen in love with Madeline Bassett, a sentimental young woman he met when he removed a thorn from her dog's foot, but he is too shy to propose. On Jeeves's advice, Gussie dresses in a Mephistopheles devil costume to attend a fancy-dress ball where Madeline will be present, the theory being that a bold disguise will embolden a timid man. Bertie considers the strategy absurd. A parallel dispute sharpens his irritation: Jeeves disapproves of a white mess jacket Bertie bought in Cannes, deeming it unsuitable for England. Bertie tells Jeeves he is taking over Gussie's case.
The fancy-dress scheme proves disastrous. Gussie goes to the wrong address, loses his money and latchkey, flees an unpaid cab driver in scarlet tights, and spends the night wandering London. Aunt Dahlia, meanwhile, insists Bertie come to Brinkley Court, her country estate in Worcestershire, to distribute prizes at the Market Snodsbury Grammar School ceremony. She threatens to ban him from the cooking of Anatole, her supremely talented French chef, if he refuses.
Bertie learns that Madeline is staying at Brinkley Court and arranges for Gussie to be invited, reasoning that prolonged proximity in romantic surroundings will give Gussie courage to propose. He also telegrams Gussie to eat sparingly so Madeline will think he is pining. In a second maneuver, Bertie persuades Aunt Dahlia to let Gussie distribute the school prizes in his place. Then a new crisis arrives: Angela and her fiancé Tuppy Glossop, Bertie's old school friend, have broken off their engagement. Bertie decides he must go to Brinkley Court.
At the estate, Aunt Dahlia explains her layered troubles. She lost a large sum at baccarat in Cannes and must confess to her husband, Uncle Tom, while extracting five hundred pounds from him to keep her women's magazine,
Milady's Boudoir, afloat. The Angela-Tuppy quarrel began when Angela recounted a frightening shark encounter while aquaplaning at Cannes, and Tuppy dismissed the creature as "probably a flatfish." The argument escalated into mutual insults and the engagement shattered. Aunt Dahlia wants Jeeves to fix everything, but Bertie insists on handling matters himself.
Bertie advises Tuppy to refuse food at dinner as a visible sign of heartbreak. He extends the same strategy to Aunt Dahlia, telling her to push away her dinner so Uncle Tom will sympathetically ask what is wrong. Dinner is dismal: Tuppy, Aunt Dahlia, and Gussie all refuse food. Afterward, Bertie takes Madeline for a garden walk and speaks of an "aching heart" in love with her, intending to prepare her for Gussie's proposal. Madeline misunderstands and concludes that Bertie himself is declaring love. She gently rejects him, then reveals her heart belongs to the man who removed a thorn from her dog's foot. Bertie realizes she means Gussie and sends him to take over.
Everything collapses. Gussie, alone with Madeline, suffers a total failure of nerve and lectures her on newts until she walks away. Worse, Anatole gives notice, insulted that course after course came back untouched as a result of Bertie's advice. Aunt Dahlia is furious.
Bertie devises two new strategies. He plans to insult Tuppy savagely to Angela, reasoning that her protective instinct will make her leap to Tuppy's defense. For Gussie, Bertie plans to lace his daily orange juice with gin before the prize-giving, concluding the man's timidity stems from being a teetotaler. Jeeves warns against it and declines to participate.
Both plans backfire. Angela agrees with every insult about Tuppy and adds more of her own, while Tuppy, hiding in the bushes, hears everything and chases Bertie in a rage. The orange juice plan goes worse. Jeeves has a change of heart and adds gin to the jug; Bertie, unaware, adds more. Gussie then independently drinks 16 gulps of neat whisky from the dining-room decanter, his first alcohol ever, and drains the spiked orange juice as well. This liquid courage enables him to propose to Madeline, and she accepts. At the prize-giving, however, Gussie delivers a rambling, uninhibited speech: He calls the headmaster a silly ass, insults Uncle Tom by name, and accuses the Scripture-knowledge winner of cheating. Madeline, horrified, breaks off the engagement.
The situation spirals. Angela gets engaged to Gussie purely as a gesture to punish Tuppy. Tuppy chases Gussie through the house; Gussie flees across the roof and ends up peering through the skylight of Anatole's bedroom, terrifying the chef and prompting him to threaten to leave once more, just after Aunt Dahlia had persuaded him to stay. Then a note arrives from Madeline: Believing Bertie proposed during their garden walk, and now disillusioned with Gussie, she announces she will marry Bertie instead.
Horrified, Bertie swallows his pride and turns to Jeeves, who proposes ringing the fire bell in the middle of the night. The domestic staff are all away at a servants' ball, so only the principals will be affected. Jeeves claims the alarm will cause Gussie to rush to save Madeline and Tuppy to rescue Angela. Bertie is skeptical but desperate. At 12:30 a.m., he rings the bell.
Everyone pours outside, but no romantic rescues occur. The front door locks behind them, all windows are barred, and the garage is locked. The group is stranded. Jeeves suggests someone ride a bicycle nine miles to Kingham Manor to fetch the key from the butler. Bertie is volunteered and rides through the dark without a lamp, only to learn that the butler left the key with Jeeves before departing.
Bertie pedals furiously home. Outside the house, Madeline asks to be released from their engagement so she can return to Gussie, and Bertie eagerly agrees. Inside, he discovers all problems have been solved: Tuppy and Angela have reconciled, Anatole is staying, and Uncle Tom has given Aunt Dahlia her cheque.
Jeeves explains his true plan. The fire bell was never meant to produce romantic rescues. Its purpose was to strand everyone outside, where their collective fury at Bertie would unite the quarreling parties against a common enemy. Sharing stories of Bertie's failings, the estranged couples bonded and reconciled. When they learned Bertie had been sent on a pointless 18-mile bicycle ride, since Jeeves had the key all along, their anger turned to amused sympathy. Bertie grudgingly acknowledges that Jeeves has fixed everything. Jeeves then confesses he "inadvertently" left a hot iron on the white mess jacket, destroying it. Too exhausted to fight, Bertie accepts the loss with a resigned "Right ho, Jeeves."