In Belfast, September 1983, in the middle of The Troubles, Sergeant Sean Duffy, one of the few Catholics in the Royal Ulster Constabulary (RUC), is drummed out of the RUC on trumped up charges.

At the same time, Dermot McCann, an IRA master bomber and ex-schoolmate of Duffy's escapes from the Maze prison and becomes a prime target for British Intelligence.

MI5 drags Duffy out of his drunken retirement to track down McCann.

The novel follows Duffy's attempts to solve a locked-room murder in order to obtain inside information on McCann's whereabouts, which finally leads to the assassination attempt on British Prime Minister Margaret Thatcher in Brighton.

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