Spoilers ahead.
Viewers were enraptured by the first season of crime drama Dept. Q, which followed irritable cold case detective Carl Morck (Matthew Goode) investigating a strange disappearance. Unsurprisingly, the season 1 finale of Dept. Q—which is based on a 10-book series by Danish crime writer Jussi Adler-Olsen—answered a ton of questions about what happened to missing lawyer Merritt Lingard, but it also brought a few more to light. Here’s what you need to know about how the first season of gritty detective drama Dept. Q comes to an end.
Merritt finally identifies her captors in the penultimate episode.
A flashback in episode 8 reveals that Merritt conspired with her high school boyfriend, Harry Jennings, to steal her mother’s jewelry in order to raise money to start a new life. However, Merritt’s younger brother, William, intervened during the robbery, which led him to become badly injured, causing a traumatic brain injury.
In the present day, Merritt figures out she was kidnapped and held hostage by Harry’s mom, Ailsa Jennings, and his younger brother, Lyle. Merritt refuses to apologize for Harry’s death, despite Ailsa’s insistence that her son would be alive if it weren’t for the robbery scheme. “Harry said she weren’t right in the head,” Merritt tells Lyle, before calling him the “psychotic brother.” After she proclaims, “Harry Jennings deserved to die,” Lyle starts trying to break the glass of the hyperbaric chamber Merritt is locked in—if successful, the sudden change in pressure will likely kill her. As he’s hitting the glass, Merritt sees Lyle’s face and calls him Sam.
Merritt trapped inside the hyperbaric chamber.
In the same episode, the detectives at Dept. Q discover that Harry’s brother Lyle had been posing as investigative journalist Sam Haig and having an affair with Merritt. The audience also discovers that Lyle and Ailsa were able to kidnap Merritt from the ferry as she’d told Sam—who was really Lyle in disguise—what time she would be traveling to Mhòr.
Lyle shares the significance of the hyperbaric chamber, and his connection to Sam.
In an old video shown at the start of the finale, a young Lyle shares that his mother used to lock him in the hyperbaric chamber as a form of torture or punishment. It’s also revealed that Lyle would regularly hallucinate Harry following his death, and at one point believed Sam, who was incarcerated with him at the same “institution for troubled boys,” was his dead brother, according to Tudum. Having been diagnosed with Enhanced Personality Disorder, Lyle remained in a mental health institution until six years ago, when he started working on the ferry to Mhòr.
Lyle and Sam reconnected as adults, which led to an unfortunate series of events. While most believed Sam had died in a tragic climbing accident, it turns out that Lyle was responsible for his former acquaintance’s death—as well as stealing his identity to get close to Merritt. Before his death, Sam also shared some details about his work as an investigative journalist, which Lyle later used to his advantage.
Lyle murders a member of law enforcement.
A local police constable on Mhòr hears Merritt’s mysterious 911 call, in which she only manages to scream, and travels to Ailsa’s residence. He finds Merritt inside the hyperbaric chamber and is approached by Lyle. “Boy, tell me I am not looking at what I’m looking at,” the officer tells Lyle. “Tell me that is not Merritt fucking Lingard.” It’s then revealed that Lyle told the police officer that Merritt fell overboard on the ferry, describing it as “poetic justice” for what happened to Harry years earlier.
“What am I supposed to do?” the officer asks Lyle, who tells him to get in his car and drive away as if nothing has happened. When the officer refuses to leave, Lyle viciously murders him with a hammer, then returns to slowly killing Merritt by altering the pressure in the hyperbaric chamber.
Harry didn’t attack and disable Merritt’s brother—Lyle did.
A flashback in episode 9 shows Merritt’s brother William hitting Harry over the head with a hockey stick, thinking he’s an intruder. While Harry is lying on the floor, William questions why he’s there, not realizing Lyle is standing behind him. Lyle proceeds to repeatedly beat William, whose serious head injuries cause lifelong damage.
The detectives in Dept. Q deduce it was Lyle who grievously injured William, not Harry. Just before Merritt disappeared on the boat, William had violently lashed out at his sister, but it wasn’t because he was angry. “You were afraid because you saw Lyle on the boat,” Akram says, showing him a picture of Lyle. William confirms the man he saw wearing a baseball cap with a picture of a cormorant on it was also Lyle.
Carl and Akram save Merritt.
The team at Dept. Q later find out that, when Lyle was a teenager, he kidnapped another kid and locked them in the hyperbaric chamber for several days. As a result, Carl and Akram decide to visit Lyle’s mom, Ailsa. Receiving no response from Ailsa’s trailer, they enter an industrial building on her land and discover the police constable who was murdered by Lyle. Nearby, they find the hyperbaric chamber and rush to the control room to try to stop the pressure from increasing and killing Merritt.
Detective James Hardy provides information about hyperbaric chambers to Carl and Akram over the phone. Before they can attempt to help Merritt, Lyle enters the control room with a gun and shoots Carl. Unbeknownst to Lyle, Akram is pretending to be dead. When Lyle approaches them, Akram stabs him, grabs the gun, and shoots, killing the kidnapper. Luckily, Carl survives the gunshot, and the pair are able to rescue Merritt from the chamber in time.
Carl and Akram interview a suspect in Dept. Q.
Merritt is carried out of building by paramedics and is greeted by her brother William, who is delighted to see her again. Lyle’s mom, Ailsa, attempts to escape Mhòr, but is apprehended as she exits the ferry. Before she can be arrested, Ailsa reaches for a gun inside her car and shoots herself in the head.
It’s business as usual in Dept. Q.
Upon returning home, Carl is greeted by his stepson Jasper, lodger Martin, and therapist Rachel, who has stopped by to leave a gift for him. Three months later, Merritt visits the police station where she thanks Carl’s boss, Moira, for reopening the investigation into her disappearance. Merritt also reveals she’s yet to meet Carl, whom she wants to thank in person. Moira says Carl is taking an indeterminate amount of time off from work, and Merritt shares her plans to return to Mhòr to spend time with brother William and their estranged father.
Carl surprises Merritt’s boss, Lord Advocate Stephen Burns, and asks him to officially allow Akram, a refugee from Syria, to become a police detective. In return, Carl promises he won’t tell anyone about Stephen’s involvement in the witness tampering that took place in Merritt’s final case before she was kidnapped. Before the episode ends, Merritt enters the basement in which Dept. Q operates, but finds the room empty. She almost bumps into Carl when exiting the elevator, but he doesn’t reveal his identity. In the final scene, Carl is shown carrying a box of cold case files to his desk and is joined by fellow investigators Akram, Rose, and Hardy.
