In the opening scene of Episode 1 of Jo Nesbø's Detective Hole, set in Oslo, Detective Harry Hole is seen reprimanding a bank robber alongside his colleague. Their car, however, collides with an oncoming tram, resulting in a severe crash. Five years later, Harry revisits the CCTV footage from the same robbery, where a bank clerk is shot by the robber for handing over the cash six seconds too late.
The Section Chief reprimands Harry for focusing on an old case and introduces him and Ellen to Beate Lønn, a biometrics expert from Stockholm. Meanwhile, Captain Tom Waaler is at the gun range, assisting a new detective with shooting practice.
At the station, Harry shares with Ellen and Beate the details of the gun used in the robbery. He reveals that it was confiscated during a drug raid and belonged to Sverre Olsen. Harry concludes that either Sverre is the suspect or is connected to the person who used the gun and sets out to find him.
Beate notes that the robber said something to the victim before shooting her, prompting Harry to ask Ellen to contact a behavior analyst. Elsewhere, Tom enquires about Harry from the junior detectives and learns that he has reopened the case. Simultaneously, Harry searches the poorer parts of the city for Sverre, questioning a group of drug users and offering them money to reveal his location.
Harry eventually reaches Sverre's hideout, where he is spotted by Sverre and he calls an unknown man. The caller warns Sverre to go into hiding and promises to purchase weapons for something significant.
This sequence of events paints a vivid picture of the investigation into the bank robbery, highlighting Harry's determination to solve the case despite setbacks and challenges. The introduction of new characters such as Beate Lønn and Tom Waaler adds depth to the story and creates a sense of urgency as the investigation unfolds.
Back at the station, Ellen and Beate delve into Harry's past, with Ellen elucidating that many hold him accountable for driving under the influence and causing the fatal crash that claimed the life of his teammate. As Tom joins them, he greets Beate, revealing their acquaintance, causing an unsettling jolt in Beate. She retreats to the bathroom before returning to scrutinize the case files meticulously.
Meanwhile, Sverre attempts to sell a stolen diamond but fails. Elsewhere, Harry meets his former therapist, Ståle Aune, and speaks candidly about his struggles at work. He reflects on his guilt over his teammate Lars' death and his ongoing endeavor to maintain sobriety.
After their session, Harry visits his girlfriend Rakel and her son, Oleg. Rakel explains that Oleg grapples with her past relationships. Harry suggests giving him space to adjust at his own pace. At the station, Ellen and Beate review CCTV footage and spot Tom in it. They inform Harry, who leaves Rakel to confront Tom. Harry and Ellen visit Tom's house, where he claims Beate is attempting to frame him and hints at past animosities between them.
Elsewhere, Oleg confides to Rakel that he's uncomfortable with Harry staying over. Meanwhile, Harry drops Ellen off at her home and they discuss his past relationships. He later returns to his apartment and pores over the case files.
Ellen tracks down Sverre's associate, Borris, and questions him about Sverre's whereabouts. At the same time, Rakel leaves Harry and Oleg at a public swimming pool to encourage them to bond. Harry shares his apprehensions with Oleg and tries to reassure him.
Ellen calls Harry to inform him that she's discovered Sverre's hideout and plans to investigate it herself, promising to call for backup if necessary. Meanwhile, Sverre contacts the unknown man and demands payment for his silence. The man requests time to respond.
Elsewhere, the Deputy Police Chief asks the Chief to recommend a successor for his position. The Chief suggests Ellen, but the Deputy Chief insists on a male candidate. Tom is then recommended.
At the same instant, Tom arrives at Sverre's secret hideout and encounters Isaksson from the Crime Department. He concocts a lie about his presence there. Back in town, Harry assists Oleg in practicing diving after the pool has closed for the day. Ellen reaches the hideout and discovers Tom inside. She attempts to call Harry but loses the signal. She witnesses Tom shooting and killing Sverre, and then attempting to flee, but Tom catches her. Harry, unaware of the situation, tries to call her as he leaves the pool.
On his way home, Harry is unable to reach Ellen and asks the Chief for permission to track her phone. Meanwhile, Ellen pleads with Tom to let her go, but he refuses and attacks her. Tom stages the scene by forcing Sverre to shoot Ellen and then killing him. He arranges the bodies to make it appear as if they killed each other.
Tom reports the incident, and the police arrive at the scene. Harry is devastated upon learning of Ellen's death and enters the cabin to see her. That night, Harry returns to his apartment and smells the liquor in his flask, as the episode comes to a close.
