Department Z has been infiltrated by a double agent and everyone is suspicious.
As once loyal friends begin to turn on each other, Agent Craigie is desperate to find the super-spies responsible. Is there an enemy within their walls? Or was Ryall, the Department man they had captured, being forced to reveal his knowledge whilst held as "a kind of prisoner"?
Time is running out for Agent Craigie if he wants to save what's left of Department Z.
A Kind of Prisoner is the 27th novel in John Creasey's Department Z series.