Recently orphaned Frank Dreyer, a gawky young man from Northern England, is invited to visit his wealthy uncle, Charles Dreyer, who resides in Munich, West Germany. Charles had taken advantage of business opportunities in post-World War II Germany to establish the Dreyer department stores, and now wonders if his nephew Frank might be a possible heir to the fortune. When blundering Frank finally arrives in Munich after missing his connecting flight in London, England, he stumbles over his suitcase at the front gate of the estate and breaks his eyeglasses. As Frank gropes his way toward the house, he is greeted by Charles’s flamboyant Italian wife, Martha, who is stunned by the young man’s clumsiness. That evening, Charles tells his wife to give the boy a chance before sending him back to England. Later, Charles introduces his nephew to the retail business, and recognizes a glimmer of potential in the awkward youth. While Martha helps Frank buy a new pair of eyeglasses and negotiates a studio apartment for him, she develops a rapport with the young man. Meanwhile, virginal Frank becomes infatuated with his aunt. One night, Frank’s next-door neighbor at the apartment, Professor Ritter, demonstrates an elastic material that he has invented called “voskin,” which resembles human flesh. Ritter wants Frank to show the sample to his entrepreneurial uncle. Looking for an excuse to visit the estate and see his aunt, Frank rushes to the house with the sample. Dressed in a negligee, Martha flirts with Frank until her husband returns home. Afterward, Frank is embarrassed by his lack of sexual experience and decides to avoid Martha, but arranges a meeting between Charles and Ritter. The professor suggests that voskin could be used to make a unique moving mannequin, but he needs financing to construct a model. Charles is intrigued with the proposal and later tells Martha that Frank may have the business instincts to be a worthy heir, after all. Inspired with an idea, Martha pays a surprise visit to Frank at his apartment. After ordering him to undress, she seduces her nephew and teaches him about lovemaking. As Martha and Frank continue their affair and meet every afternoon, Charles believes that his wife is busy with church charity meetings. Before returning home, Martha always leaves a note for Frank while he is sleeping. Meanwhile, Charles is excited by Ritter’s progress with the mannequins and wants to reward Frank with an executive position for introducing the voskin idea to the company. During one of their afternoon trysts, Martha tells Frank that she does not love Charles and married the wealthy Englishman when she was a poor Italian war refugee. However, Frank becomes anxious when she hints that Charles could unexpectedly die. While hosting a party at the estate, Charles plays a practical joke on the guests by turning off the lights and pretending to be an intruder. During the confusion, Martha notices that Frank is very protective of her. Later, Charles informs Martha that he is taking a ski vacation alone, but he secretly brings along two mistresses, Isolde and Ida. While he is away, Martha persuades Frank to kill her husband, and they discuss different methods of murder. While they frolic in the bedroom, Charles arrives home a week earlier than expected, but Frank manages to slip away from the house without being noticed. At a demonstration of the voskin mannequins, Charles is furious when the professor’s prototypes malfunction in front of potential buyers. That evening, Martha notices her husband’s stress and suggests they take a seaside vacation with Frank on the French Riviera. Although he reminds his wife that neither one of them can swim, he agrees to the trip. The next day, Frank is not at home when Martha arrives for their afternoon rendezvous. She is excited to tell him about their travel plans and begins to undress. While rushing home to meet Martha, Frank encounters Charles in the street, and his uncle insists on seeing the apartment. Martha hears her husband’s voice in the hallway and bars the door. Just as she is about to be discovered, the landlord, Enricht, says that Frank’s girl friend is waiting inside. Laughing, Charles says goodbye to his nephew. On the way out, he asks Ritter about Frank’s lover. Unaware that Martha is Charles’s wife, the professor says that she is a sophisticated, older woman with black hair. Based on Ritter’s description, Charles thinks the look would make an ideal voskin mannequin. The professor agrees to have the model ready when Charles returns from France. Later, Ritter finds a photograph of Martha in Frank’s apartment to construct the new mannequin. Meanwhile, Martha tells Frank that drowning will be the perfect murder. When they arrive for the seaside vacation, Martha plots to push Charles overboard during a rowboat excursion, but Frank is nervous and secretly wants to cancel the plan. After Martha persuades her husband to join her and Frank in the rowboat, Charles announces that tomorrow he will return to Munich to sign a contract for the voskin mannequins, which will earn him a fortune. Subsequently, Martha tries to stop Frank from knocking Charles overboard. In the confusion, Frank loses his eyeglasses and tips the balance of the boat, inadvertently causing the three of them to fall into the water. Charles and Frank survive, but Martha drowns. After the funeral, Frank appears less naïve and develops the manners of an arrogant executive. When his uncle assures him that he will inherit the business, Frank moves into the estate. Later, landlord Enricht delivers Frank’s love letters from Martha that were left in the apartment, but Frank is able to destroy them before Charles discovers their content. Meanwhile, Ritter also arrives at the estate to show Charles the new voskin mannequin, a perfect likeness of Martha.