The ninth episode of "Only Murders in the Building" commences with a haunting flashback, revisiting a moment before Lester's tragic demise. There, we're introduced to Lester, the robot, as he and Miller stand in contrasting presence with the human Lester who vehemently opposes the use of the robotic entity. Yet, we overhear the robotic Lester recording every nuance around him, even in its sleep mode. A chilling clip shows robot Lester capturing Randall's secretive stash of a bloody elevator crank.
Returning to the present, Mabel, Charles, and Oliver confront Randall about the elevator crank, but he swiftly eludes them. Unable to pursue him further, they decide to vacate the Arconia building now that Camilla is taking over. Robot Lester reminds them of their impending deadline to evacuate, while Mabel texts Jay amidst the preparations.
As Oliver, Mabel, and Charles gather to discuss their future living arrangements—now that the building is transforming into a Casino—Oliver announces his plans to relocate to New Zealand. Charles, on the other hand, reveals his intention to move into a spa that resembles a nursing home. Mabel's dejected state becomes evident as she struggles to find a suitable place for herself.
In the lobby, Mabel encounters Teddy, fresh out of prison and ready for the move-out. She discloses her impending shift in focus from investigating the murders now that Detective Donna has arrived.
Meanwhile, Oliver, still unpacked and procrastinating, informs Charles of his plan for a farewell party for the residents. Charles declines the invitation, as he embarks on a quest for new hobbies and friendships. Just then, Mabel and Donna share a drink in the gaming parlour, where Mabel reveals her conversations with Jay and her contemplation of dating him.
Mabel makes a startling discovery: a secret door that leads them to a chamber connected to Nicky's dry cleaning shop. Realizing that Randall has been hiding in plain sight within the building all along, Mabel shares this revelation with Oliver and Charles, leading to a confrontation with the elusive culprit.
Randall, steadfast in his silence about the night of the murder, is driven by his promise to Lester. However, the Robotic Lester unleashes a trove of footage from that fateful night, replaying the scene where Lester carries the bloodied elevator crank to the doorman's changing room. Randall's gaze lingers, questioning: "Have you taken a life?" Lester implores Randall to keep silent on this matter and tasks him with delivering the shrimp to Oliver's room. Lester claims to have saved Arconia from oblivion.
Fast-forward to the present, Randall reveals that Lester's act of killing Nicky was a desperate bid to save Arconia. The quartet, along with the other residents, vows to uncover Lester's murderer and avenge his memory. That very night, Charles finds solace in Howard's words of loneliness.
Charles empathizes deeply with Howard's plight and apologizes for being a poor neighbor. He agrees to join Oliver's party as Jay arrives to pick up Mabel for their Maldives adventure. Mabel, with a sharp eye for details, confronts Jay about his suspicions in Lester's murder, refusing to sweep things under the rug and closing the door on his attempts at charm.
As the party rages on, Howard reveals that the marks on Charles' floor resemble those of a motorized wheelchair. Charles, Oliver, and Mabel realize that Nicky's mother also used a motorized scooter. The episode concludes with the trio confronting Mrs. Caccimelio over her theft of the finger, their determination fueling the fire of their quest for justice.
