After her once-happy marriage dissolves, a former detective grapples with jealousy and anger while returning to work to hunt down a serial killer.
Marcella is desperate to remember what happened at Grace's. Meanwhile, she sees patterns that convince her the killings are linked to her old case.
The team learns of Marcella's ties to Grace. Jason's affair comes to light at DTG. Peter Cullen remains Marcella's focus in the Grove Park murders.
There's an unexpected break in the Grove Park murders, but not everything adds up. Marcella goes on her own to find out details about Grace.
Marcella plays a cat-and-mouse game with Peter Cullen. New details of Grace's case lead to shocking connections. Jason's mistake could prove fatal.
The outcome of one of the cases sends Marcella over the edge. Tim suspects a suicide was really murder. A past tragedy haunts both Jason and Marcella.
Yann is now a prime suspect, but Marcella has her doubts. Tim and Marcella grow closer, while Tim's investigation into Barnes's death unsettles Jason.
Marcella questions Henry about Matthew. Doubts about an alibi lead her to ask Jason for help. A violent confrontation sets the endgame in motion.
A gruesome find inside the wall of a flat opens an old wound in Marcella's son. After learning of Marcella's blackouts, Jason issues an ultimatum.
Marcella learns pedophile Phil Dawkins is linked to senile rocker Reg Reynolds. A second body is found. Leo's postmortem turns up an eerie discovery.
Phil Dawkins's address is leaked to the press. Jason makes an announcement that spurs Marcella to see a hypnotherapist. The killer's captive escapes.
Marcella links a teen's disappearance to Reg Reynolds and recovers a shocking memory from her last blackout. A vengeful Dawkins targets Marcella's son.
The blue lorry's tachograph allows police to home in on the area where Adam was held captive. Caregiver Gail receives a message from her patient Joel.
A lineup leads to the arrest of a suspect, who drops a bombshell on Marcella. A confession letter arrives. Marcella develops a new theory on the killer.
After learning why Nigel lied, the police launch a rescue operation. When KidsCall is linked to another body, Marcella figures out the killer's motive.
Eric's arrest leads Marcella to Gail's workplace, where she makes a dreadful discovery about Joel. Under hypnosis, Marcella remembers Juliet's death.