Larry Lipton, an editor at HarperCollins, and his wife Carol have a pleasant encounter in the elevator with older neighbors, Paul and Lillian House.

When Carol brings the widower a dessert, she finds a crematory urn under his kitchen sink that contradicts his story about Lillian's burial.

Carol decides to investigate and steals the key to the House apartment from the super, entering when Paul is away and snooping to find two tickets to Paris and hotel reservations with a woman named “Helen Moss.” Carol dials the code for the last number dialed, and the phone is answered by someone saying “Waldron”.

Paul returns while Helen is snooping, narrowly missing her hiding under the bed, but she manages to sneak out undetected.

Marcia theorizes that the dead body was Lillian's wealthy sister, who resembled her and had a heart attack while visiting the Houses.

Marcia devises a plan to trick Paul into incriminating himself by using Helen, someone he trusts, to claim she saw Lillian’s unincinerated body.

At the run-down second-run movie theater Paul owns, where Carol is being held, Larry dodges Paul’s bullets in a film noir chase parody echoing the in-process showing of Orson Welles's The Lady from Shanghai during a similar shootout-in-a-room-full-of-mirrors sequence in the film.

Allen started Manhattan Murder Mystery as an early draft of Annie Hall, but he did not feel that it was substantial enough, and he decided to go in a different direction.

[3] The role of Carol was originally written for Mia Farrow, but the part was recast when she and Allen ended their relationship and became embroiled in a custody battle over their three children.

[6]Making the film was a form of escape for Allen because the "past year was so exhausting that I wanted to just indulge myself in something I could relax and enjoy".

After getting over her initial panic in her first scene with Alan Alda, Keaton and Allen slipped back into their old rhythm.

Allen had cinematographer Carlo Di Palma rely on hand-held cameras, "swiveling restlessly from one room to another, or zooming in abruptly for a close look."

[1] Zach Braff, who was 17 years old at the time, appeared in one scene as Nick Lipton, the son of Larry and Carol.

[12] In his review for Newsweek, David Ansen wrote, "On screen, Keaton and Allen have always been made for each other: they still strike wonderfully ditsy sparks".

[14] Janet Maslin called it a "dated detective story" but also wrote, "it achieves a gentle, nostalgic grace and a hint of un-self-conscious wisdom".