The Ambler Warning book by Robert Ludlum

On Parrish Island, a restricted island off the coast of Virginia, there is a little-known and never-visited psychiatric facility. There, far from prying eyes, the government keeps in "deep storage" former intelligence employees whose psychiatric state make them a security risk to their own government, people whose ramblings might jeopardize ongoing operations or prove dangerously inconvenient.One of these employees, former Consular Operations agent Hal Ambler, is one of the few who is so dangerous that he is in complete isolation from other patients, kept heavily medicated and closely watched. But there's one critical difference between Ambler and the other patients in the facility: Ambler isn't crazy.

With the help of a sympathetic nurse, Ambler manages to first clear his mind of the drug-induced haze and then executes a daring escape. On the loose and barely one step ahead of the retrieval teams sent after him, he is out to discover who had him stashed in the psychiatric hospital and why.

But the world he returns to isn't the one he so clearly remembers - friends and longtime associates don't recognize him, and there are no official records of any person named Hal Ambler. With no resources and his unknown enemies closing in on him, Ambler has to uncover the truth of who he was and figure out what it is about him - remember what he knows - that makes him such a danger that someone is willing to risk everything to see him dead.