In season 4, a bombing detonates personal secrets, rocking Slough House's already unstable foundations.
A London bombing puts Taverner under pressure. When River grows concerned for his grandfather, Louisa encourages him to go for a visit.
A naive agent makes a discovery about the Westacres bomber. Lamb suspects that David knows more than he's letting on.
River is trapped in France. Back at Slough House, the Dogs have come for Lamb.
Taverner is desperate to hide dangerous secrets. River seeks answers at his grandfather's house.
Lamb questions David about France as River comes face to face with the enemy.
Impossible decisions are faced and sacrifices are made.
