Walter Mitty imagines himself to be the Commander of an enormous Navy hydroplane in the midst of the worst storm in twenty years. He is brave and competent, barking orders and reprimanding his subordinate, Lieutenant Berg, for offering his opinion. The rest of his crew follows his orders without question, in full faith that “the Old Man” will get them through the storm, full speed ahead.   

Mrs. Mitty interrupts Mitty’s daydream, telling him to slow down. The couple are driving into Waterbury to run their weekly errands. Mrs. Mitty senses that Mitty is tense and wishes he would go to Dr. Renshaw for a physical exam. 

When Mitty drops his wife off for a haircut, she reminds him to buy himself new overshoes, which he does not want. She responds by insinuating that he does need them since he is no longer a young man. She also chastises him for not wearing his gloves, suspecting that he has lost them. Mitty puts on his gloves, but immediately removes them as soon as he is out of her sight. 

As Mitty drives past a hospital, he slips into another daydream. In this one, he is a world-famous doctor. He arrives at the operating room only to learn that the four doctors assigned to the patient’s case are stumped. A life-saving device begins to malfunction, but Mitty uses a fountain pen to improvise a temporary fix. The doctors beg Mitty to take charge of the operation, and he does. 

Mitty’s medical drama is interrupted by the shouts of the parking lot attendant who tells him he is entering the lot through the exit-only lane. The young man embarrasses Mitty by parking his car for him. This incident causes Mitty to recall a time when he had to be rescued by a tow truck driver after he had tried to remove his car’s snow chains and wound up wrapping them around the car’s axles. 

After purchasing overshoes, Mitty tries to recall what Mrs. Mitty instructed him to pick up at the grocery store. A newsboy, shouting news about the Waterbury trial, triggers another daydream. Mitty is the defendant in a murder trial. He remains calm in the face of an aggressive district attorney. Instead of denying his skill with firearms, Mitty brags about his expertise. This upsets his lawyer and throws the courtroom into chaos. A young woman falls into Mitty’s arms, and he defends her from the district attorney.

Mitty comes out of the courtroom drama by declaring “puppy biscuits,” the item he had forgotten. A woman passing by laughs at his outburst. He moves on to the hotel where he has agreed to meet Mrs. Mitty. 

As he waits, he reads a magazine article about Germany’s superior air force. It alarmingly asks if it will be the key to Germany conquering the world. Mitty’s mind drifts into a fantasy in which he is a World War I pilot. In a dugout besieged by enemy bombardment, Mitty volunteers to fly a solo mission to bomb an enemy target. He casually downs shots of brandy while a lower-ranking officer warns him of the great danger. Unfazed, Mitty departs to face almost certain death. 

A hit by Mrs. Mitty brings Mitty back to reality. She chastises him for being difficult to find and ignores him when he asks why she never considers that he might be thinking. She dismisses his comment, insinuating that he must be ill.

Walking back to the parking lot, Mrs. Mitty stops at a drugstore to pick up a forgotten item. She orders Mitty to wait for her outside. As Mitty lights a cigarette and leans against the store’s exterior wall, it begins to rain. Mitty slips into his last fantasy of the story. He faces a firing squad, condemned to death for an unstated crime. He refuses the customary blindfold, defiantly confronting his imminent death, “undefeated” and “inscrutable.”