In this crackerjack Cold War thriller, MI5 faces a deadly threat, one only Richard Knox can avert. But he only has six days and the clock is ticking fast.

How long can you survive in the shadows?

Richard Knox, freshly returned to active duty after a year out of the field, is ordered to uncover the invisible enemy that's infiltrated the Service in his absence.

His quest takes him to Hong Kong, a city on the brink of chaos, where he discovers the lines between friend and foe have never been more blurred.

Who is behind the assault on MI5? How long have they been operating in the shadows? And what is their endgame?