Episode 10

Tom Quinn has been told, in plain terms, to end things with Christine Dale. He doesn't, which is its own kind of loyalty problem. Then Christine hands him a secure CIA communication she received by accident: an American assassin is in the UK for a hit, and the CIA means to take him out without telling Five or any of the security services. Tom can't take that to Harry, not without explaining where it came from, so he brings in Danny and Zoe instead.

It's an hour of smoke and mirrors, and it earns the name. The plan comes apart almost as soon as it starts. Every step Tom takes to manage the crisis without admitting how he knows about it makes the next step harder, and the assassin moves through London on a schedule nobody controls. The hour keeps coming back to one uncomfortable idea: Tom has crossed a line, and keeping the secret may have turned him from an asset into a liability.

Matthew Macfadyen plays Tom at the point where stubbornness curdles into something more dangerous. Megan Dodds's Christine is the one who sets everything in motion with a misdirected message. Tomas Arana's Herman Joyce, Samantha Coughlan's Lisa Joyce, Mac McDonald's hard-faced man and Elizabeth Chambers's woman fill out the American side of the story. Peter Firth is Harry, Keeley Hawes is Zoe, David Oyelowo is Danny, Shauna Macdonald is Sam. Howard Brenton and David Wolstencroft wrote it; Sam Miller directed.

Spooks is at its best when trust is the rarest commodity in the room, and this episode has almost none to spare. But the real weight lands on Tom. He started the hour keeping a secret to protect someone, and he ends it wondering whether he has become exactly the thing Harry always warned him about. The title's promise holds: by the end, you are not entirely sure what you actually saw.