In "Inside No. 9" Season 9, therapist Blake Chambers brings home Drew, the father of a former patient who died under Blake's care. Drew seeks revenge, forcing Blake into a horrifying choice: save his son, Robbie, by confessing his past exploitation, or let Robbie die to protect his reputation. Blake chooses inaction, leading to Robbie's death. Later, Jason, in a coma, navigates an escape room that represents his mind, narrowly waking up as his family prepares to withdraw life support. Finally, a piano tuner tricks a woman into taking on a cursed symphony, resulting in her horrific death. The season concludes with the show's creators reconciling, deciding to make a "No. 9 bus episode."

Season 9 of Inside No. 9 covers episodes 1-6. Here's everything that happened:

Season 9, Episode 1: Boo to a Goose - A diverse group of passengers is stranded on a broken-down underground train when a purse is stolen during a blackout. Tensions rise as they debate who the thief is, revealing their prejudices and willingness to conform. The "replacement service" arrives, revealing itself to be a shadowy organization that replaces dissenters with obedient clones. Those who challenged authority are killed by toxic gas, while the compliant survivors are spared.

Season 9, Episode 2: The Trolley Problem - Therapist Blake Chambers (Steve Pemberton) saves Drew (Reece Shearsmith) from a bridge, bringing him home. Drew, however, reveals he is the father of Blake's former patient, Ellie, who died by overdose after Blake exploited her and failed to intervene. Drew seeks revenge, forcing Blake to confess. The episode culminates in a horrifying twist where Drew, having buried Blake's son Robbie alive, sets himself on fire, leaving Blake with an impossible "trolley problem" choice: save his son by exposing his crimes, or let Robbie die to preserve his reputation. Blake chooses to do nothing, sealing Robbie's fate.

Season 9, Episode 3: Mulberry Close - New residents Damon and Val are observed by nosy neighbours via a doorbell camera. After Val disappears and their dog Popcorn is found dead, neighbour Larry murders Val with a brick, believing she poisoned his pet. The camera reveals another neighbour accidentally killed Popcorn, culminating in a Netflix true crime documentary.

Season 9, Episode 4: CTRL/ALT/ESC - Jason, his wife, and daughters enter an escape room, "The Killer's Lair." The game is revealed to be a manifestation of Jason's mind as he lies in a coma, with his family preparing to withdraw his life support. Solving the final puzzle, Jason identifies "IX" and wakes from his coma, narrowly averting the withdrawal of life support.

Season 9, Episode 5: Curse of the Ninth - Edwardian piano tuner Jonah Quigley is ensnared by Lillian Burnham, who seeks to profit from her late composer husband's cursed ninth symphony. After a scuffle leads to the maid Devonshire's death, Jonah seemingly completes the work. He cunningly tricks Lillian into adding the final page herself, causing Lillian to die horribly from the curse, leaving Jonah to escape.

Season 9, Episode 6: Plodding On - At a wrap party for "Inside No. 9," fictionalized Steve Pemberton and Reece Shearsmith face a potential split as Steve considers a lucrative Amazon project, leaving Reece behind. After a montage of past episodes, Steve loses the Amazon deal, leading to a heartfelt reconciliation. The duo decides their next project will be the long-awaited "No. 9 bus episode," titled "Plodding On," celebrating their enduring partnership.