Investigations into the ambassador's death reach the highest corridors of power. Helen pays a risky visit to an old friend, and Sam faces a tough choice.

Cast: Keira Knightley, Ben Whishaw, Sarah Lancashire, Andrew Buchan, Andrew Koji, Omari Douglas, Kathryn Hunter, Sam Troughton, Ella Lily Hyland, Gabrielle Creevy, Isabella Wei, Agnes O'Casey, Finn Bennett, Adeel Akhtar, Tai Yin Chan, Dan Li, Charlotte Rice-Foley, Taylor Sullivan