Plot: We open on the shore with waves gently rolling on to a beach, then a boat gently bobbing on the ocean. Robert Scott Carey (Grant Williams) narrates a few lines, "The strange, almost unbelievable story of Robert Scott Carey, began on a very ordinary summer day. I know this story better than anyone because I am Robert Scott Carey." Carey and his wife of six years, Louise (Randy Stuart) are resting on the bow of his brother's boat.
They are on vacation and soaking up some sun. Louise goes below to get Scott a beer. A strange cloud or patch of fog approaches. Scott attempts to make his way below, but the shimmery fog coats his head and body with what appears to be glitter before he can do so.
Six months later the milkman makes his morning delivery to the Carey home. Louise gives the cat some of the milk then goes into the house to finish preparing breakfast. Scott asks about his clothes. They are too loose. Pants and shirts are too large. He is losing weight and chides his wife about her cooking as the cause. He asks Louise to pick up a bathroom scale.
Increasingly concerned, he visits his family physician, Dr. Arthur Bramson (William Schallert) and is told his height measures five-feet and eleven inches. Scott informs the doctor, "I've been six foot, one-inch since I was seventeen." The doctor chalks his weight loss up to overwork and stress. He reassures Scott that, "People just don't get shorter." A week later Scott notices even his bathrobe doesn't quite fit right.
When Louise suggests a visit to the doctor, Scott informs her he saw a doctor a week ago. They prepare for bed and he kisses his wife and notices he's getting shorter. He gets in bed and plays with his cat, Butch. He returns to see Dr. Bramson again. Now Bramson has a series of X-rays taken at different times to compare. He confirms that Scott is indeed getting smaller. He is at a loss to explain why.
He refers Scott to the California Medical Research Institute. More tests and X-rays follow. Dr. Thomas Silver (Raymond Bailey) tells Scott that he is losing vital chemical elements, Nitrogen, Calcium and Phosphorus. The doctor does find something that doesn't belong--he describes it as an anti-cancer. The doctor asks about exposure to insecticide. Scott tells him two months before he passed a truck on the highway that was spraying trees.
Next the doctor inquires about a radioactive exposure. Scott says no, but Louise reminds him of the mist on Charlie's boat six months earlier. The two different exposures combined to start a process in Scott's body that causes him to shrink. Scott and Louise get in their car. They talk about the implications of his condition and their marriage. Before they drive off, Scott's wedding ring falls off his shrinking ring finger.
His brother, Charlie Carey (Paul Langton), stops by the house to inform Scott that the loss of a major account means no more paychecks. Charlie suggests Scott, now about the size of a five year old, make the nosy reporters pay for his story. In debt and now unemployed, Scott does sell his story. Louise calls the telephone company and asks for an unlisted phone number. Outside a crowd of reporters and gawkers try to see Scott.
Louise informs her husband that they must wait for an unlisted line. Scott overreacts and directs his anger at Louise. Their marriage is starting to show signs of stress. Scott's behavior towards her, the incessant phone calls, and the pounding on their front door is too much for Louise. She begins sobbing. She tries to reassure Scott that the doctors are working on an anti-toxin.
Scott keeps a journal. He notes today's numbers--his height (36 ½ inches) and weight (52 pounds). Louise is in the basement working on a dress. The phone rings, Scott answers, and tells his wife, "The anti-toxin, they found it." Dr. Silver injects Scott and reminds them both that there is no guarantee. He gives the odds as 50/50. Scott must stay at the institute for a week. The next week Scott, Louise, Dr. Silver and his nurse (Diana Darrin) meet.
The nurse reports Scott is the same height and weight as a week before. Dr. Silver tells Scott it seems the process has stopped, but re-growing back to a normal size is an entirely different matter. Scott becomes morose; His marriage is deteriorating. He grabs his coat and leaves the house. He walks over to a carnival. The Carnival Barker (Frank Scannell) introduces one of his acts, a 36 ½ inch midget. Scott realizes the world sees him as a freak.
He leaves the carnival without entering and walks over to a Café for coffee. He sits at a table and is greeted by a woman, Clarice Bruce (April Kent). Her friend (Billy Curtis) reminds her not to be late for the show before he leaves the café. Clarice joins Scott at his table for coffee. She tells him she was born a midget. She tries to reassure him that life is worth living. She leaves for her show.
The outing helped Scott's mood, "That night I got a grip on life again. I went back to work on my book. It absorbed me completely". Sometime later he shows the journal to Clarice in the park. It improves his mood greatly. But as they get up off the bench, Scott notices he's shorter than Clarice. "It's starting again." He panics and runs off.
Scott is now living in a doll house. The house shakes as Louise walks down the stairs. Louise calls out to him and he walks out onto the balcony to speak to her. She informs him she's going out shopping. He reenters his doll house and shuts the door. Louise opens the front door, and then returns to the desk for something. Butch the cat slips in unnoticed. She leaves the house and closes the door. Scott is now about six inches tall.
He knows his behavior is worse. He is more tyrannical and demanding with Louise. He contemplates suicide, but he still has hope for a medical cure. The cat sniffs around the doll house. Scott tries to nap inside. He hears the cat sniffing. He picks up a makeshift knife and goes to the door. He opens it. The cat snarls at him. He slams the door shut. Butch goes to an open window of the doll house and paws inside. He scratches Scott.
The cat manages to pull the doll house away from the wall enough to get inside. Scott exits and runs under a chair. The cat knocks him down and begins to toy with his potential meal. Scott spots the lamp cord and the lamp on the table above dangerously close to the edge. He pulls the cord, topples the lamp which scares off the cat. This gives him a chance to escape to the basement.
He pushes the door closed on the cat, but before he can close it completely the cat pushes back. Louise, re-entering the house, allows a gust of wind to blow the basement door open and flings Scott down into Louise's sewing basket. Louise sees the cat and immediately runs to find Scott. She finds the doll house askew from the wall and Scott missing. She finds the toppled lamp and a scrap of Scott's clothing smeared with blood. She concludes the cat ate her husband.
A KIRL news report is broadcast, "From Los Angeles today, a tragic story. The passing of Robert Scott Carey. The report of the death of the so called Shrinking Man comes from his brother. Carey's death was the result of an attack by a common house cat--a former pet in the Carey home." Charlie is with Louise and a nurse (Helene Marshall). The nurse tells Charlie that Louise is barely resting despite a sedative.
Down in the basement, Scott regains consciousness in the sewing box. He employs a champagne cork to climb up to an opening in the box. He makes it to the basement floor. He's now about three inches tall. He realizes he can't scale the stairs. He calls to his wife, but she can't hear him. A dripping hot water heater provides a source of water, and a match box a shelter. Next on the agenda is a source of food.
He uses a nail to cut up his clothes. Charlie talks to Louise about her future. Louise thinks Scott could be alive, but Charlie is sure he is dead. Louise dwells on the circumstances. Charlie makes real estate arrangements for the house. Without food Scott realizes the shrinking process is accelerating. He sees a piece of cheese in a mouse trap. He employs a nail to spring the trap, unfortunately the action causes the cheese to roll into a floor drain.
He sees a chunk of cake high on the basement wall. He tries to figure a way up to it. A spider is on the prowl on the basement floor. Scotts sees it and runs. He finds a pin cushion in Louise's sewing kit and grabs a pin as a weapon. He takes another pin and bends it into an "L" shape. He ties thread around it. He uses a match to burn the thread to length.
He uses his new tool as a grappling hook and scales the thread progressively upwards to the top of a box. Using a paint stick he gets to the other side of the box. He scales a loose piece of string from a ball of string to get to the top of the basement wall. A spider web is partially anchored to the piece of cake. He uses the pin to break off chunks of the stale cake. He sees a basement vent screen and approaches it.
The grid is too small to slip through. He weeps in frustration. "My prison, almost as far as I could see. A gray friendless area of space and time," he laments. Scott returns to the cake. He throws a couple of chunks over the wall to the basement floor below. The largest piece is entwined a spider web.
He repels down the string. He takes his prize in hand and is chased by the tarantula. He escapes into the relative safety of his match box home. The spider can't get in and leaves. "In my hunt for food, I had become the hunted," he wryly observes.
Charlie descends the stairs carrying Louise's suitcases. She tells Charlie she wants a small trunk located in the basement. The hot water heater leak grows larger, now dripping on Scott's match box home. The dripping wakes Scott. He goes out to investigate as the hot water heater leaks becomes a torrent. He is washed off the platform and is washed down towards the floor drain.
Charlie and Louise enter the basement and see the flooding. Scott calls out but they can't hear him. Charlie removes some rags that clogged the drain. He picks up the trunk and tells Louise, "I want you packed and out of this house tonight." Scott uses a pencil as a life preserver. Charlie and Louise drive away from the house.
Scott regains consciousness over the drain. He is cold and wet and faces his old enemy, the tarantula, again. He sizes up his situation. He still has his weapons he retrieved from his matchbox. Scott becomes more philosophical and determined to get that last piece of cake. He makes it back to the top of the basement wall and his food. He plans to use scissors as a weight and his pin and thread to skewer the spider.
He picks up a couple of rocks and throws them at the spider. He pulls on anchor threads starting a vibration of the web. The spider descends to the source of the disturbance. It chases Scott who prepares his weapons. He spears the spider, and then pushes the scissors over the ledge. But the string snags on a piece of jagged concrete. The string snaps and the spider continues to chase Scott. Using his other pin he fends off the spider's advance.
He runs, but trips and is held down with his pin just out of reach. He manages to work himself free, retrieves his pin, and plunges it into the spider's thorax. It impales itself on the pin. Scott is victorious. Scott walks slowly over to the cake. He breaks off a chunk, and then drops it. He realizes he no longer feels hunger or fear of shrinking. He walks back up to the vent screen, drawn by the light coming in.
Scott is now less than an inch tall. He gets through the screen and walks outside looking up at the darkening sky and the full moon. He walks through the yard looking up at the stars. We close with pictures of various types of galaxies and Scott tells us, "To God there is no zero. I still exist."