When a guest dies mysteriously in her house, the intrepid Eileen "Bundle" Brent seeks out to find his killer- only to be drawn into a labyrinth of secret societies and international espionage. Eileen "Bundle" Brent is intrigued by the death of a young man in her bedroom, and is determined to find answers.The novel opens at a party in the mansion of the Marquis of Caterham, who has rented it to a wealthy businessman and his wife, Sir Oswald and Lady Coote. There are also three young women and four young men. One of them, Gerald "Gerry" Wade, tends to regularly sleep very late in the day. The other six youngsters plan a joke on Gerald by putting eight alarm clocks in his room after he is asleep.
The joke takes a macabre turn when, after Gerry sleeps through all of the alarms, the guests that learn he has died of an overdose of chloral. The clocks have been arranged on the mantelpiece, but one of them has been thrown from the window, leaving seven clocks. Ronny Devereux and Jimmy Thesiger, two of the young men at the party, drive to see Gerry's half-sister, Loraine, and break the news to her. Ronny hints at something about Gerry to Jimmy but does not fully confide in him. It is shown that Jimmy and Loraine are in love.
After the Marquis and his family move back to their mansion Eileen “Bundle” Brent, the Marquis' daughter, finds an unfinished letter from Gerry to Loraine in her room, asking her to “"forget what I said about that Seven Dials business." One of her friends, Bill Eversleigh, was also at the party. She decides to meet with him in London. On the way, Bundle hits a man with her car. He mutters “Seven Dials...tell...Jimmy Thesiger” before dying. She brings the body to a doctor, who says that the man had been fatally shot before she hit him. The body is identified as Ronny Devereux's.
When Bundle returns home, she learns that a threatening letter was sent to George Lomax, a prominent politician of her acquaintance, from the seedy Seven Dials area of London. The next day Bundle meets with Loraine and Jimmy at Jimmy's apartment, and tells them of Ronny's death. Jimmy tells them about Ronny's strange behavior before. Loraine tells them that she found a list of names and numbers along with an address in Seven Dials-a seedy area of London- in one of Gerry's letters, and that he alluded to a secret society. The three speculate about whether Gerry was murdered. Bundle tells them about the letter Lomax received. They decide to go to a party that Lomax will be holding at his home, Wyvern Abbey.
Bundle meets with Police Superintendent Battle, asking him about criminal organizations based in Seven Dials. He humors her, but does not take her concerns seriously. He hints that Bill Eversleigh might know something. Bundle meets with Bill, who reluctantly tells her that the Seven Dials is a shady nightclub. At Bundles's insistence, they go there the next night. At the club, Bundle hides in a concealed closet to overhear a secret meeting. Five people are gathered around a table, wearing masks with clock-faces. They refer to themselves as an organization called the Seven Dials. She can hear that they are all of different nationalities by their accents. She notices that one woman has a black mole on her shoulder blade and speaks with an Eastern European accent. It is mentioned that two of their number are missing, putting the group at seven members in total. They talk about George Lomax's upcoming party, a German inventor named Eberhard, and Sir Stanley Digby, the Air minister. They also say that a German footman in their pay named Bauer will be at the party.
Jimmy and Bundle later discuss what she saw. Jimmy tells Bundle that Eberhard has invented a specialized kind of steel, which the British plan to buy. They guess that the Seven Dials are planning to steal the plans for the invention at Lomax's upcoming party.
At the party Loraine, Bundle, Jimmy, and Bill meet the beautiful Hungarian Countess Radzky, the German inventor Eberhard, and the new German footman Bauer. That night, gunshots are heard. Jimmy says he tried to shoot the burglar, but he escaped. The plans are missing. Bundle notices that the Countess has a mole in the exact same place as the mysterious foreign woman she saw in the Seven Dials meeting, and concludes that is the same woman. When Bauer is also discovered missing, she concludes that they are in it together and that Bauer stole the plans.
After a few weeks, Bill visits Jimmy, telling him that he received a letter from Ronny Devereux's lawyers. Ronny had left it to be sent to Bill should something happen to him. Bill tells Jimmy he is unable to believe its contents.
A few hours later, Jimmy calls Bundle and Lorraine and tells them to meet Bill and himself at the Seven Dials club. Bundle shows Jimmy the secret cupboard where she hid earlier, while Bill waits in the car. Lorraine goes out to speak to Bill, and when she comes back she says that something is wrong with him. They find Bill unconscious. Bundle goes to find brandy while Jimmy goes to find help. She is then struck unconscious by an unknown person.
Bundle regains consciousness as Bill holds her. Before she opens her eyes, she hears him declare his love for her, believing that she is still unconscious. She is surprised and delighted at the confession. She awakens, to Bill's relief.
Bill tells her that the Seven Dials is not a criminal organization, but a secret society of criminal-catchers headed by Superintendent Battle himself, to which Bill and the late Ronny Devereux also belonged. The Countess Radzky is also a member, but is actually the American actress Babe St. Maur in disguise. The Seven Dials were on the tail of an international criminal specializing in the theft of intellectual property. The infamous thief was none other than Jimmy Thesiger. He and his accomplice Loraine were arrested that afternoon.
Bill explains that Jimmy killed Gerry Wade when he realized that Gerry was onto him. Ronny had taken the eighth clock to see if anyone would pick up on the “Seven Dials” clue. Jimmy killed Ronny when he came too close to the truth. Bauer had been planted by the Seven Dials to attempt to thwart the thief, but he was not successful. Together Jimmy and Loraine stole the plans, and Jimmy fired the gunshots and invented the story of the robber who escaped. Bill had invented the story of the letter to force Jimmy's hand. When Jimmy gave Bill a drink at his flat, Bill correctly guessed it had been drugged and did not drink it, feigning unconsciousness. It was Jimmy who had struck Bundle. He intended to leave them in the club to frighten the Seven Dials members, but Bill managed to have Jimmy and Lorraine arrested first.
Bundle takes Ronny's old place in the Seven Dials, and she and Bill become engaged.
Best part of story, including ending:
The story is very humorous and light. Though the clues are plentiful, they are subtle and clever.
Best scene in story:
The opening scene at the party is the most humorous, Christie uses a very light-hearted, understated humor in this opening scene that is very unlike her later novels.
Opinion about the main character:
Bundle is incredibly courageous and intrepid, placing herself in dangerous situations. However, she draws all the wrong conclusions and trusts Jimmy entirely too easily.