The episode commences with a surreal, dreamlike sequence that plunges Mabel into a subconscious labyrinth. She gives birth to triplets: a microphone, symbolizing her podcasting obsession, and baby versions of Charles and Oliver's heads. The dream, as bizarre as it may seem, serves as a metaphor for the trio's intertwined lives and their shared passion for true crime.
Returning to reality, we find Oliver recuperating after his cardiac event. The trio wastes no time in diving back into the investigation to clear Loretta's name. As they gather at the Arconia, they receive a series of deliveries, including Joy's discarded wedding dress and a case of Schmackary's cookies from Donna, the show's producer. These seemingly unrelated items will later prove to be crucial clues in solving the mystery.
The trio begins by questioning Dickie, Ben's brother, who has a solid alibi: he spent the night getting wasted and visiting a brothel. Intrigued by this revelation, they decide to investigate the brothel, only to discover that it's actually a fabric store. The "whores" are elderly seamstresses who had helped Ben with his costumes. The seamstresses reveal that Ben had confided in them about feeling isolated and alone, suggesting that he may have been seeking solace in their company.
Flashbacks to the sitzprobe provide additional clues. We see how Ben's argument with Loretta escalated and how Charles intervened. We also witness the tension between Ben and Donna, who had received a negative review of the show. It is revealed that Donna had read the review and was determined to sabotage Ben's performance.
Donna's motive becomes clear: she wanted to protect her son, Cliff, whose reputation was tied to the success of the show. By eliminating Ben, she could prevent the show from being a failure and preserve Cliff's career.
As the trio ponders the evidence, Mabel has a breakthrough. She realizes that Ben had written a message on his mirror using lipstick: "Fucking pig." She connects this message to the negative review that Donna had read and concludes that Donna was the one who wrote it.
With this new information, the trio is able to piece together the final events of the night. Donna had planted a poisoned cookie in Ben's dressing room, hoping to weaken him. When the cookie failed to kill him, she pushed him down the elevator shaft.
In a dramatic climax, Mabel, Charles, and Oliver race to the courthouse to stop Loretta from pleading guilty. Dressed in Joy's wedding dress, Mabel manages to convince the judge to postpone the arraignment. With their evidence, they are able to expose Donna as the murderer.
The episode ends on a hopeful note as the trio celebrates their victory and the strength of their friendship. However, the lingering question remains: will the trauma of the past year change their lives forever?
"Thirty" is a satisfying conclusion to a season filled with twists and turns. The episode not only resolves the central mystery but also provides closure for the characters and the audience.