Diana Taverner

Diana Taverner runs Regent's Park with the cool precision of someone who has never once mistaken decency for a useful quality. As First Desk, she plays intelligence services and government against each other, treating Slough House and its washed-up agents as pieces to be moved rather than people to protect. She wants control, and she gets it.

Kristin Scott Thomas plays her without a wasted gesture, all clipped vowels and unreadable calculation, so that every scene becomes a negotiation you can't quite follow until it's over. The writing never explains her motives outright, trusting the performance to make ruthlessness look like competence — which is far more unsettling than villainy would be.