Marcella's mental stability has always been tenuous, and this continues in season 3. The series finds her undercover in Northern Ireland, having gotten inside and apparently joined a powerful criminal family there, the Maguires. She now goes by the name of Keira Devlin and is backed by a mysterious handler, who, we will find, has past ties to the Maguires. Headed by a ruthless matriarch played by a chilling Amanda Burton, the Maguires seem like an untouchable group in Belfast, and Marcella's goal is to sow suspicion and discord among them. There are two brothers, one sister, and the sister's husband, and there are pathologies aplenty in the family for her to exploit. The mother, however, is quite balanced, and though one of the sons views Marcella as his girlfriend, the mother never particularly trusts Marcella and watches her every move closely.
From its start, Marcella has been a crime show of the sort where the detective has as many, if not more, mental problems than the people she is pursuing. River, with Skellan Skarsgard, was another example of this. Anna Friel must love playing Marcella; she gets to play an absolute, brilliant mess of a person in a way most roles don't offer. What's interesting is that over the course of the series, instead of showing us a person who makes progress with her issues, or learns to sort of limit or compartmentalize her issues, as Skarsgard's John River in fact does, Marcella in certain ways only seems to be getting more unbalanced with each new season. We've learned a root cause of what has created such guilt and anguish and mental imbalance in her, and in Season 3, she is fighting with herself as fiercely as she is struggling to keep her machinations against the Maguire family from going awry. While all of this does, at times, strain credulity, it makes for a dark and tense drama. Will Marcella destroy the family or implode? Can she keep things together enough to do her job. She is a brilliant cop, no question of that, but she is also, in some ways, her own worst enemy. Self-destructive tendencies in the tormented detective is nothing new, but Marcella at times takes these tendencies to a whole new level, and after the way Season 2 ended, on such a harsh and unexpected note, you really do feel that the makers of this show may take Marcella to the point of actual no return.
Will they do a Season 4? I don't know but I hope so. I'd watch it, though I wonder what identity the fluid (read unstable) Marcella will have this time.