Gamache, Myrna, Lucien, and Benedict visit Bertha’s neighbor, Patricia Houle, who recognizes Gamache and has been to Myrna’s bookstore many times. She confirms that she knew her neighbor as the Baroness and clarifies that the nickname was self-appointed. Patrice witnessed Bertha’s will, and when they ask about the Baroness’s competence, Patricia says she was clearheaded, though eccentric.

Myrna, remembering Patricia’s past book purchases, deduces that she is interested in poisonous plants. Patricia confirms this and reveals that the Baroness also maintained a poison garden, pointing out that foxglove is digitalis and identifying other toxic plants like monkshood, lily-of-the-valley, and hydrangea.

They return to the Baumgartner farmhouse, which is tilting dangerously under the weight of new snow. Gamache decides to call the township to have it inspected and condemned. After digging out the cars, he stops Benedict from driving his pickup truck because it lacks winter tires. Benedict is stubborn until Gamache identifies himself as head of the Sûreté du Québec. Benedict, shocked, submits. Gamache offers to pay for winter tires in exchange for a promised driving lesson.

As Myrna drives Benedict back to Three Pines, she reflects on the poison garden and thinks the real danger comes from things you cannot see, like bindweed moving underground.

Gamache visits Isabelle Lacoste, one of his senior officers, who is recovering from a severe head wound sustained during the raid months earlier. She asks about the internal investigation, and their conversation turns to the problem of missing carfentanil. Gamache confirms that a large quantity of opioids has disappeared in Montréal.

They discuss the trauma of their injuries. Lacoste becomes frustrated when her unsteady hand spills coffee. Gamache comforts her by sharing his own struggles after being shot. He explains his mentor’s philosophy that life is like a longhouse where all experiences reside forever, and one must make peace with the past.

Gamache reveals another problem: The Sûreté Academy wants to expel Cadet Amelia Choquet, a former sex worker and substance user whom he recommended for admission because she is brilliant. Opioids were found in her possession. Gamache is afraid that if she is expelled, she will relapse and die. Lacoste reflects that Gamache’s belief in second chances is both an advantage and a disadvantage. This would be Amelia’s third chance. Lacoste worries that believing someone capable of redemption when they have proven otherwise is dangerous.

Gamache and the Commander of the Sûreté Academy meet with Cadet Amelia Choquet. She is defiant, nervously clicking her tongue stud, which Gamache has learned through his acquaintance with her is an unconscious distress signal. When she is shown the narcotics found under her mattress, she denies ownership. Gamache notices her dilated pupils and accuses her of being high. She claims that she used eyedrops but threw them away.

When asked where she got the drugs, Amelia accuses Gamache of responsibility for the opioids he allowed into the country, calling him a ruin and a failure. After she waits outside, Gamache speaks with the Commander of the Academy. He proposes expelling her without offering rehabilitation, arguing that she is not ready for the academy and would waste a spot another person could use. The Commander argues that they have a responsibility to help her, and abandoning her will kill her.

Twenty minutes later, Amelia is expelled. As she passes Gamache and the Commander, she turns and throws a book at Gamache—Marcus Aurelius’s Meditations, which she had bought after refusing Gamache’s copy. After she leaves, Gamache quietly calls in and instructs two police officers to follow her. The Commander realizes that Gamache is planning to use Amelia and follow her to the drug traffickers.

Meanwhile, Myrna receives a call from Lucien Mercier, arranging the meeting with the Baumgartner heirs for that afternoon. In his car, Gamache opens Amelia’s book and finds a line she underlined about fearing never beginning to live rather than death.

Gamache arrives at Anthony Baumgartner’s home for a meeting with Bertha’s three children: Anthony, Caroline, and Hugo. They are surprised that the liquidators didn’t know their mother. Gamache notices a photograph of the three siblings as children.

Caroline reveals that their mother believed she was descended from the Rothschild banking family through her grandfather, a Kinderoth. Hugo supports the claim, but Anthony dismisses it as a fantasy that drove their parents apart. Lucien reads the will, which leaves $5 million and properties to each child, with the title passing to Anthony. The siblings react with sadness rather than disappointment, their emotions focused on their mother’s imagined vast fortune and what it did to her. They discuss the farmhouse: Hugo wants to save it, but Caroline has no sentimental attachment. They recall that their father died in a combine accident 36 years earlier; Anthony, then 16, found the mangled body. Gamache examines a family photograph featuring the Baroness.

Gamache, Myrna, and Benedict return to the bistro, where power and phones have been restored. Benedict reports that the garage cannot tow his truck until tomorrow. Reine-Marie invites him to stay another night. The group discusses the meeting. Myrna compares the Baroness’s fantasy to the movie Harvey, about a man whose best friend is an invisible giant rabbit. Benedict wonders if there is harm in believing in a fortune that does not exist.

Beauvoir and Annie arrive in Three Pines with their son, Honoré. The village is walled in by towering snowbanks. In the study, Gamache asks about Beauvoir’s meeting with the Sûreté investigators. Beauvoir inadvertently reveals that there was a second, undisclosed meeting. He admits that they offered him a way out and implied that Gamache would be blamed for the opioid crisis. Gamache accepts that he had falsely hoped to be exonerated and that the blame is rightfully his alone. He has no regrets, knowing that his family is safe.

Meanwhile, Amelia Choquet arrives at her old rooming house in Montréal. The landlady gives her a squalid room and leaves a mop and pail, indicating cleaning is her job in exchange for rent. Disgusted, Amelia kicks over the bucket and leaves to search for the carfentanil.

Gamache takes Beauvoir for a walk outside under the aurora borealis. He asks about the other meeting. Beauvoir lies, saying it was with his and Annie’s bank about buying a house. Gamache looks at him steadily. Beauvoir feels he is drifting away from his father-in-law, and he knows Gamache understands that Beauvoir is being offered a way to save himself at Gamache’s expense.

The next morning, the household discovers that Benedict is missing. His bed is undisturbed, but his belongings remain. A village-wide search begins. At the bistro, Gabri reveals that Billy gave Benedict a ride to the Baumgartner farmhouse to pick up his truck the previous night. Myrna calls Benedict’s cell phone but gets voicemail. Gamache is concerned because Benedict promised not to drive his truck, which lacks winter tires.

Gamache, Myrna, and Beauvoir drive to the farmhouse and find that it has collapsed. A second, unfamiliar car is in the yard. After honking, they hear knocking from inside the rubble. Billy Williams arrives, feeling responsible for dropping Benedict off. Gamache, Myrna, and Billy enter the unstable structure while a claustrophobic Beauvoir waits for the rescue team.

Inside, debris blocks their path. Myrna uses a jack to lift a beam, creating a narrow opening. They squeeze through and locate Benedict, who is emotional but unhurt. As the Sûreté rescue team arrives, the rest of the house collapses. Benedict pulls Gamache into a sturdy doorway, and Billy pulls Myrna, saving their lives. Pinned in the rubble but alive, Gamache looks past the doorway and sees a gray hand protruding from the debris.

Amelia wakes in Marc’s bed, disoriented and in pain. Marc is an old friend from childhood who has a substance addiction.

The night before, Amelia went to Marc for help finding the carfentanil. She told him about the missing opioids Gamache allowed through and proposed that they take over the market. They immediately went out to try to find the dealer who has the drugs. Amelia was confronted by an aggressive dealer, but she used techniques learned at the Sûreté Academy to choke him nearly to death, then stole his drugs. She declared herself to be the “one-eyed man” and told the dealer to warn his supplier. She gave Marc most of the stolen drugs.

In the present, Amelia cannot remember what happened after confronting the dealer or how she returned to Marc’s apartment. Marc says he found her passed out in an alley. She experiences a recurring hallucination of a little girl in a red tuque holding a bag of dope. Marc tells her that she has made a strong impression on the street, and everyone now wants to know who she is. He has been telling people she is the “one-eyed man,” establishing her reputation in the criminal underworld.