Marcella is shocked to the core of her being when her husband Jason leaves her unexpectedly, confessing he no longer loves her. Heartbroken, Marcella returns to the Met’s Murder Squad. Ten years ago Marcella gave up her fast-tracked police career to marry and devote her life to her family. With the abrupt end to her marriage and isolated from her 13 year old daughter and 10 year old son, Marcella throws herself into work to stop herself from falling apart.
Eighteen months later, Marcella has a new life as a deep undercover operative in Belfast, spying on a powerful family that's running a shady business.
Marcella is recognized on the street, and later finds an odd note on her windshield. When DCI Sangha arrives in Belfast, Bobby must cover his tracks.
Marcella receives an anonymous package. At Jessie's vigil, DCI Sangha spots an eerily familiar face. Finn finds out who sold Jessie the heroin.
The Maguires arrange for Bobby to leave the U.K., but the plan goes awry en route to the airport. Katherine sends a threatening message to Marcella.
Her stalker's latest threat leaves Marcella suspicious of Frank. After recognizing one of Bobby's abductors in police records, she tracks him down.
Marcella recalls how Frank rescued and reprogrammed her 18 months earlier. When Stacey flees from the Maguires with her baby, Marcella must find her.
Finn uses Rory's phobia to bully him into an alliance. Marcella confronts Frank with a discovery about his past. DCI Sangha learns of Stacey's arrest.
Marcella's latest blackout leaves her with an unexplained corpse. Wondering why DCI Sangha is still in Belfast, Jack decides to investigate on his own.