In the late 1930s, just before Christmas, renowned radio personality Sheridan Whiteside finds himself an unplanned guest at the home of Ernest W. and Daisy Stanley in Mesalia, Ohio. After a slip on the icy steps results in a supposed dislocated hip, Whiteside commandeers the first floor, relegating the Stanleys to the second level of their own home. His overbearing presence turns their lives upside down, as he threatens legal action to ensure his demands are met.

The Overbearing Guest

Whiteside is no ordinary houseguest. He is a domineering figure, using his sharp tongue and relentless will to manipulate those around him. His nurse, Miss Preen, often finds herself the target of his biting sarcasm, while others, like Dr. Bradley, are deceived by his false flattery. Whiteside’s complete disregard for the feelings and convenience of others leaves the household in disarray.

Managing Chaos

Despite his brash demeanor, the Stanleys attempt to accommodate Whiteside’s peculiarities. They endure the influx of unusual deliveries, including a crate of penguins and a "cockroach city," as well as a procession of eccentric visitors. This array of characters even includes convicts from Whiteside’s favored charity, the Crockfield Home.

Interfering in Lives

As the holiday draws near, Whiteside’s meddling extends beyond mere inconvenience. His interference in personal matters begins to have far-reaching consequences. He sets his sights on the Stanleys’ household staff, Sarah and John, attempting to lure them away with promises and compliments. Simultaneously, he advises the Stanley children, Richard and June, to pursue their dreams without regard for their father’s wishes.

Complicating Relationships

Maggie Cutler, Whiteside’s dedicated assistant, falls for Bert Jefferson, a local journalist and budding playwright. Faced with the prospect of losing Maggie, Whiteside devises a sly scheme to sabotage her budding romance. He invites the alluring actress Lorraine Sheldon to town, hoping her presence will distract Jefferson.

Counter Schemes Unfold

Maggie, realizing Whiteside’s plan, enlists the help of Beverly Carlton, a talented impersonator. Carlton poses as Lord Botomley, Lorraine’s coveted suitor, to divert her attention. However, Whiteside quickly uncovers this ploy, leaving Lorraine disillusioned and Maggie on tenuous ground once more.

Complications Arise

Whiteside’s plans begin to unravel as Dr. Bradley reveals that Whiteside’s injury was a misdiagnosis. Seizing the opportunity, Whiteside temporarily silences the doctor with empty promises of collaboration. Meanwhile, Mr. Stanley’s patience runs thin, and he takes decisive action by involving law enforcement to evict Whiteside.

A Last-minute Ploy

In a desperate bid to stay, Whiteside threatens to expose Mr. Stanley’s sister, Harriet Sedley's criminal past as an ax murderer. This revelation halts Mr. Stanley's eviction plans, though tensions remain high.

A Christmas Resolution

On Christmas Day, Whiteside experiences a rare moment of generosity, aided by his friend Banjo. Together, they devise a plan to eliminate Maggie’s rival, Lorraine, by placing her in an Egyptian mummy case intended as a gift. Banjo, with the help of deputies, whisks her away to an awaiting plane, bound for Nova Scotia—thus clearing the path for Maggie’s happiness.

A Tumultuous Departure

As Whiteside prepares to leave, the Stanleys anticipate a return to normalcy. Yet, fate intervenes as Whiteside slips on the porch, requiring yet another stay. His immediate call for Miss Preen and threats of a new lawsuit leave Mr. Stanley in exasperation and Mrs. Stanley in a faint, highlighting the continuous cycle of chaos Whiteside brings wherever he goes.