As the Only Murders in the Building crew takes refuge on Long Island at the home of Charles’ sister, Doreen, they find themselves in a precarious situation – being the main target of a murderer. The trio, comprised of Charles, Oliver, and Mabel, is joined by the actors playing them in the film production, Eugene Levy, Eva Longoria, and Zach Galifianakis. The actors, who have been following the investigation, offer their services to help unravel the mystery. Initially, Mabel is hesitant to accept their involvement, but after some sage advice from Loretta, she decides to task the celebrities with making sense of the evidence they have collected so far.
The actors successfully piece together several clues that the trio hadn’t previously noticed, tying back to the first season of their podcast and the show itself. They focus on the unresolved poisoning of Oliver’s dog, which was initially attributed to Sting but was never officially solved. They also examine the note left on their door, “End the podcast or I end you,” which was assumed to be left by Jan but is revealed to be written by someone left-handed. Additionally, they highlight the note left on Jan’s door, “I’m watching you,” which Jan would not have needed to leave as the killer.
The new evidence prompts Charles to remember Sazz’s notes, which hinted that she had figured out that someone was stalking the Arconia crew for a long time. This revelation opens up the investigation in a whole new direction, suggesting that the killer has been following them for a significant amount of time with a long-term motive for hurting them.