Larry Lipton, portrayed by Woody Allen, and his wife Carol, played by Diane Keaton, return home from a hockey game in Manhattan. Inside the elevator, they unexpectedly encounter their elderly neighbors, Paul Jerry Adler and Lilian Lynn Cohen House, whom they barely know. This chance meeting leads to an invitation for drinks at the Houses’ apartment, where it becomes apparent that Larry works in publishing while Paul owns a dilapidated cinema undergoing renovations. Though married for twenty-eight years, Paul and Lilian are childless, contrasting with Larry and Carol, who have a son away at college.
The night following their drinks, Larry and Carol join friends Sy Ron Rifkin and Marilyn Joy Behar at the cinema to watch Billy Wilder's classic, Double Indemnity. Upon their return, a shocking scene awaits them: the Houses’ door is ajar, surrounded by neighbors. They learn that Lilian has mysteriously died of a heart attack, startlingly unexpected since she seemed quite healthy just days prior.
In the following days, while heading to the Met, Carol begins to find Paul’s buoyant demeanor a bit unsettling. During dinner with their friends, including Ted (portrayed by Alan Alda), conversations spark doubt about the authenticity of Lilian's death. Carol speculates on the absence of any known heart condition, and Ted muses darkly that Paul might have had a hand in his wife's demise to be with “his tootsie.” While Larry dismisses these notions as unfounded, Carol’s suspicions only grow.
Determined to confront her doubts, Carol crafts a dessert for Paul but discovers unsettling evidence in his apartment: a hidden funerary urn, contradicting Paul's claim that Lilian was buried. Late into the night, her suspicion escalates when she overhears Paul’s cryptic phone conversation, and later still, she bravely sneaks into his place after swiping a spare key from the building super, Jack William Addy. Inside, she uncovers plane tickets to Paris for Paul and a woman named Helen Moss, which only intensifies her concerns.
In a twist of fate, Carol teams up with Ted to track down Helen Moss, realizing she’s a young actress and discovering Paul’s relationship with her. A chance visit to the cinema exposes Paul’s plans to profit from selling the property, revealing a complicated web of deceit. Their investigations lead them to eerie truths, culminating in the chilling discovery of Lilian’s body hidden in a hotel room, only to have it vanish by the time the police arrive.
As events spiral into a chaotic investigation riddled with red herrings and twists, Larry and Carol navigate a series of close calls, including a failed attempt to confront Paul. Tensions rise as long-buried feelings simmer between them; Larry becomes ensnared in self-doubt about his marriage, while Carol grapples with her attraction to Ted.
Ultimately, they concoct a devious plan to bait Paul into revealing his treachery. Under the guise of an audition for Helen, they stage a fake scenario, hoping to trap him into a confession. A perilous confrontation unfolds at the theater, where a confrontation ensues, leading to unexpected outcomes involving love, loyalty, and immense personal growth as secrets unravel.
In the end, the story loops back into romance, as Larry and Carol find themselves rediscovering their love amidst the chaos, while Marcia's clever machinations draw another couple together, revealing that life can bring surprising love from the depths of intrigue. As the dust settles, the couples emerge, transformed and ready to embrace their futures together.
