A bumbling nobleman tries to kill his rich uncle in a series of elaborate traps.

In the face of rising taxes and escalating expenses, Sir Henry Clitterbern, the master of Clitterbern Manor, finds himself in debt. Henry thinks that his salvation lies in an inheritance from his seventy-five-year-old uncle George, who left England years earlier to seek his fortune in America. When George notifies the family that he is coming home for a visit, Henry envisions a doddering old man and plans a premature death for his ailing uncle. Upon learning of Henry's intentions, his sister Marjorie suggests that the family's financial difficulties could be overcome if Henry's son Albert would just get a job, but Henry, a confirmed member of the landed gentry, sputters that "he will not prostitute his son to trade." On the day of George's arrival, Henry instructs Albert to make sure that the car breaks down in the woods after picking his uncle up in town. Once Albert gets out of the car and walks a safe distance from George, he is to signal by waving his scarf, after which Henry, hidden in the brush, will shoot George and earn a tidy inheritance. Henry's plan goes awry, however, when Albert's car is sideswiped by another vehicle that then crashes through the guard railing. Edward, the driver, was on his way to visit his sweetheart, Henry's daughter Constance, and now finds himself pinned himself inside the wrecked vehicle. George sends Albert for help, and as he trudges along the road, Albert absentmindedly removes his scarf just as Marjorie peddles by on her bicycle. Spotting the waving scarf, Henry fires his rifle, killing Marjorie. That night, as Henry and his wife Edith discuss their anticipated millions, Alice, Henry's eccentric second cousin, overhears their conversation. The next morning, while watching Albert spray his plants with poison, Grannie conceives of slipping some into George's tea, but Henry vetoes the idea. At tea time, after Grannie criticizes George's "newfangled" tea bags, George challenges her to taste his tea. As the family intently listens to the bespectacled criminologist Edward deliver his treatise about the psychology of crime, Grannie, unaware that Edith has infused George's tea with a dose of poison, takes a sip and keels over dead. When the family goes on a fishing trip and picnic, Henry decides to use the occasion to drown George and instructs Albert to row George down river in a boat, then capsize the craft, making sure that George hits his head on a rock and sinks to a watery grave. The plan goes amiss, however, when Albert falls overboard instead and George accidentally cracks him over the head with an oar. Although William Gilrony, a virile young man standing on the shore, spots the floundering Albert and pulls him from the icy waters, soon after, Albert succumbs to pneumonia and dies. One day, when George insists on "toughening up" the bookish Edward by taking him hunting, Henry gleefully rigs a booby-trapped rifle in the storeroom, aiming the muzzle at the door and tying a string to the trigger, assuring that George will meet his maker when he opens the door to return his weapons. Upon returning from the hunt, George goes to the storeroom while Henry smugly waits, listening for a gunshot. As he is about to open the door, George is distracted by a crashing sound coming from his room. There he finds Alice, who offers to show him a secret passage to the storeroom. When George appears in the living room after safely stowing the guns, Henry, incredulous, climbs a ladder to the roof to peer through the storeroom window. While Henry gazes at the still-rigged rifle, George removes the ladder to examine a bird's nest in a tree. Without looking, Henry begins to climb down the now-missing ladder, topples from the roof and breaks his arm. Still determined to exterminate George, Henry pries loose a step in the stairway that George descends on the way to his nightly raid of the refrigerator. That night, instead of visiting the kitchen, George goes with Alice in search of an owl, leaving an unsuspecting Edith to tumble to her death on the faulty step. Later, when Constance informs Henry that Edward suspects foul play may be involved in the epidemic of family deaths, Henry becomes alarmed. Soon after, Edward arrives with the police, prompting Henry to make an abrupt departure. Hurrying to the storeroom to fetch his suitcase, Henry opens the door and is greeted by a blast from the rifle. At the inquest into Henry's death, Edward asserts that George killed Henry. Alice then innocently states that all the deaths occurred as a result of Henry's attempts to kill George. Some time later, a now-married George and Alice sail aboard a luxury liner, smiling and toasting each other.