Merritt Lingard was a successful lawyer who disappeared while on a ferry trip with her brother William. The incident happened four years before the events shown in Dept. Q. At the time, the police couldn’t find enough proof to explain what happened.
No body was ever found, and the case was eventually closed without answers. When Department Q takes over the case, the story begins to unfold in new and unexpected ways.
Also Read: Alien: Earth – Every creature and species spotted in the latest trailer
Early suspicions point toward her brother and past legal enemies

William, her brother, was with Merritt on the ferry when she vanished, so he became a prime suspect in Dept. Q’s reopened files. He had faced emotional challenges for years and was recovering from an accident that had changed his life.
Detectives learn that Merritt’s career as a prosecutor created tension with people she prosecuted. One notable figure was Graham Finch, a wealthy businessman she failed to convict in a high-profile murder case. These factors cast suspicion on William, Finch, and others.
Dept. Q reveals a hidden relationship that becomes the turning point in the case
As the investigation continues, the Dept. Q detectives uncover that Merritt maintained a secret relationship with a man she believed to be journalist Sam Haig, only to realize that Haig had perished in a climbing accident long before their meeting.
The imposter had assumed Haig’s identity to deceive her. This revelation clarifies for the investigators that her disappearance resulted from a deliberate and premeditated plot, rather than an accident or coincidence.
Lyle Jennings is revealed as the person behind the kidnapping in Dept. Q

The man pretending to be Sam Haig is revealed to be Lyle Jennings, someone from Merritt’s past. Years ago, Merritt had blamed Lyle’s brother during a robbery incident, which led to serious consequences.
Lyle held a grudge against her and decided to get revenge. He kidnapped her and kept her hidden in a high-pressure chamber at a private facility. No one could find her because he ensured there was no trace of evidence.
Also Read: Why Georgie and Mandy's first marriage Season 2 must finally give Audrey McAllister the spotlight
Merritt is rescued after four years, and the case finally closes

With the help of clues and careful planning, the Dept. Q team finds out where Merritt is being held. They manage to rescue her safely from the chamber, unharmed.
Merritt survives, but she avoids speaking to her rescuers, likely because of the trauma she went through. The police also discovered corrupt officers who tried to stop the investigation. In the end, the case is closed, and the department gains more support to continue solving cold cases.
Dept. Q unfolds at a steady pace and with clear focus, guiding viewers through each twist with careful precision. The investigators pay close attention to small clues that might otherwise be overlooked. Dept. Q never sensationalizes events but instead shows how persistence and teamwork help solve the mystery of Merritt Lingard’s disappearance.
The series highlights the importance of examining every lead and questioning every assumption. This approach lets the audience follow the investigation in a logical, step-by-step manner without feeling rushed.
Also Read: How every character’s story ends in The Handmaid’s Tale finale