In 1924, prize-winning novelist Kit Marlowe returns to her home town to give a lecture and is greeted by her old friend, Millie Drake.  In the years since they last saw each other, Millie has married and is now pregnant with her first child, news that Kit learns first from Millie's husband Preston.  At first Millie is upset that Kit does not seem eager to see her, but later, after Kit apologizes, Millie confesses that she too has written a book designed to be a best seller.

Eight years later, Millie is a wealthy and successful writer of popular fiction.  She and Preston and their eight-year-old daughter Deirdre are in New York City to attend the opening of Kit's play.  Millie's success has helped destroy her marriage, however, and the afternoon before opening night, Preston, who is drinking heavily, tells Kit that he is in love with her.  Replying that Millie would always be between them, Kit tries to patch up her friend's marriage, but Preston leaves Millie after asking Kit to keep an eye on Deirdre.

Ten years later, after the bombing of Pearl Harbor, Kit joins the Red Cross and broadcasts a request for money over the radio.  Preston, who is now in the army, hears Kit's speech and telephones her. Kit agrees to join him for a drink, sending Rudd Kendall, her younger lover, to fetch Deirdre as a surprise for Preston.  Preston surprises Kit as well when he announces his engagement.

The next morning, Rudd, having received his commission, begs Kit to marry him immediately.  Because of the difference in their ages, Kit turns him down, and a disappointed Rudd joins the now-grown Deirdre for a walk.  The two spend the day together and fall in love.

In the meantime, Kit changes her mind about Rudd and reveals her plans to marry him to Millie.  After Preston tells Millie he is remarrying and wants to see Deirdre more often, he confesses that he was once in love with Kit.  Overcome with jealousy, Millie tells Deirdre about Kit's marriage plans and then accuses Kit of stealing her husband.  Fed up with her friend's tantrums, Kit gives Millie a thorough shaking.

That night Rudd breaks the news to Kit that he has fallen in love with Deirdre.  Although it is a shock, Kit pretends to be delighted and rushes off to make sure that a disillusioned Deirdre does not miss her chance for a happy marriage.

Later, Millie stops by Kit's apartment to apologize and Kit forgives her. Millie then describes her new book, Old Acquaintance, about two longtime women friends, and the two women drink to it.