Henry Graham (played by Walter Matthau) is a scion of a patrician New York family who spends months dodging his attorney’s calls until a blunt verdict lands: he has squandered his entire inheritance and is utterly broke. With his future laid bare, he confides in his loyal valet Harold (George Rose) and hears a bold, morally dubious suggestion: marry into wealth to secure his survival. Desperate, he secures a $50,000 loan from his avaricious uncle Harry (played by James Coco) and sets himself a hard limit: he has six weeks to find a wealthy wife and repay the loan, or lose everything—including a roughly $500,000 art collection.
In a bid to salvage his fate, Henry spots Henrietta Lowell (played by [Elaine May]), a botany professor who is clumsy, painfully shy, and immensely wealthy, with no family. At a society party, she embarrasses herself by spilling tea on the carpet; Henry defends her, offers her a ride home, and pretends to share interest in her field. She reveals a grand ambition to discover a new plant species and name it after herself, and the two strike a pact: they will marry within the week.
Their union is met with resistance from Henrietta’s skeptical lawyer Andy McPherson (played by [Jack Weston]), who schemes with Uncle Harry to derail the marriage. Yet Henrietta’s guileless nature proves a steady match for their plots, and her openness makes Henry reconsider his motives. When Henry finally reveals the loan and the six-week deadline, he admits that his initial plan was to settle his debts and take his own life, but meeting Henrietta has given life a new purpose. Henrietta, in a rare display of generosity, says she will clear his debts before the wedding and will grant him unrestricted access to her bank account, effectively making him financially independent and blurring the line between need and greed.
The couple marry and embark on a Caribbean honeymoon, where Henrietta’s mind turns toward her work as she contemplates a potential new fern species. Upon their return, Henry takes charge of Henrietta’s disordered life, dismissing 17 household staff who had colluded with Andy to drain her funds, and begins to straighten out her accounts while secretly plotting to rid himself of her. But his plan to poison her with garden pesticides is foiled when he discovers her organic garden uses no dangerous chemicals.
Henrietta learns that Henry holds a BA in history, and she suggests he teach at her university, a role he initially resists. He toys with Harold about disposing of his wife, and Harold confesses that caring for Henrietta has changed him—tending to her has given Henry a new sense of purpose and competence.
A breakthrough comes when Henrietta’s fern is named Alsophila grahami in her honor, a gesture that deeply moves Henry. She invites him on her annual field trip to the Adirondacks, where a canoe expedition ends in trouble: the pair are overturned, Henrietta cannot swim, and Henry contemplates abandoning her. Yet a drifted fern specimen—the plant she named after him—reminds him of the life they could share. He rescues her, chooses to stay by her side, and vows to be there for her, even hinting that he might teach history after all.
