
Following on from the dramatic conclusion of the previous series, season 3 sees Marcella in Belfast as an undercover detective. She has taken on a new identity, Keira, and has infiltrated the infamous Maguire crime family but as she investigates their activities, questions come to the fore about how much she’s embraced the Keira personality and left Marcella behind.

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.