Thoroughly Modern Millie

In 1922 New York, Millie Dillmount arrives determined to become a stenographer for a wealthy employer and to marry well. She embraces a strictly modern, independent mindset and declares she will not settle for less. This sets the stage for her ambitious search through a city full of temptations.

Miss Dorothy Brown checks into the Priscilla Hotel and befriends Millie. When the housemother Mrs. Meers learns Dorothy is an orphan, she notes the loneliness and vulnerability. Unbeknownst to Millie, Mrs. Meers schemes to traffic vulnerable tenants.

Mrs. Meers' scheme to kidnap orphans is exposed through her dealings with Bun Foo and Ching Ho. She targets women with no family, using the hotel as cover. Millie remains ignorant of the danger lurking behind the scenes.

At a Friendship Dance in the Priscilla's dining hall, Millie meets Jimmy Smith, a devil-may-care paperclip salesman. The two instantly spark a playful, flirtatious connection. The encounter marks Jimmy's entrance into Millie's world as a potential romance.

Millie lands a job at Sincere Trust and fixates on Trevor Graydon, a handsome but self-absorbed supervisor. Meanwhile Jimmy shifts from casual flirtation to genuine interest, creating a growing love triangle. The pursuit of wealth and romance collides with Millie's developing feelings for Jimmy.

On a Long Island outing, Jimmy brings Millie and Dorothy to meet eccentric widow Muzzy Van Hossmere. Jimmy reveals that his father was Muzzy's former gardener, adding a hint of social distance and humor. Millie starts to fall for Jimmy, but misreads his closeness with Dorothy and grows uneasy.

Millie dresses as a flapper and makes a bold attempt to seduce Trevor, hoping to clinch a marriage for money. The plan backfires as Trevor remains unmoved and aloof. Disappointment stiffens Millie's resolve to stick to her original scheme.

Trevor meets Dorothy and immediately falls for her; Dorothy reciprocates. Millie watches the love blossom around her, left heartbroken and realizing her plan may fail. The rival romance shifts the dynamics of the trio.

Jimmy's attempts to talk to Millie are blocked by Miss Flannary, the stern head stenographer. He climbs up the side of a building to reach her and plead his case. Millie tells him she is quitting now that Trevor is no longer available.

Mrs. Meers makes several attempts to kidnap Dorothy, but Millie disrupts each plan. Trevor sits in his car, drinking and lamenting Dorothy's apparent betrayal. The couple's heartbreak deepens as the truth about the disappearances remains hidden.

Millie finds Dorothy's room empty and realizes Dorothy has vanished. Jimmy arrives, and together with Trevor, they piece together the mystery. They discover that the missing girls share a common trait and suspect Mrs. Meers.

Jimmy disguises himself as a woman named Mary James to gain access to the Priscilla and draw out Mrs. Meers. Millie, trying to stay inconspicuous, accidentally triggers a fireworks display outside the building. The explosions set the captives free and lead Millie, Dorothy, and Jimmy toward safety.

Chased by Mrs. Meers and her henchmen, Millie and friends reach Muzzy Van Hossmere's Long Island mansion. Under Muzzy's leadership, they subdue the villains and secure everyone's safety. The danger ends with a newfound sense of family and purpose.

In a final revelation, Millie learns Jimmy is actually James Van Hossmere and Dorothy is his sister, with Muzzy as their stepmother. The truth shifts their goals toward love rather than wealth. Millie marries Jimmy, Dorothy marries Trevor, and Muzzy marries one of her instructors.