MI5 Intelligence Officer Liz Carlyle feels marginalised when her boss Charles Wetherby pulls her out of the Counter Terrorist Committee and tasks her to investigate a tip that years ago the IRA planted a sleeper in one of the branches of British Intelligence. To Liz, who had been involved in tracking terror cells posing a major threat to the security of the nation, the danger posed by an IRA sleeper seems minimal. But Liz is proven wrong. The sleeper is no longer working for the IRA; his fanatical hatred of the British has led him to team up with Britsh born Al Qaeda supporters. He is their planner, their Mr Big. And they have a plot to destroy a major British establishment. It is essential that Liz discovers who this sleeper is and gets inside his mind, to figure out the target and the terrorists' ingenius plan to circumvent the tight security. The lives of the very flowering of British youth are at stake.