London, October 1984: Irish terrorists have blown up British Prime Minister Margaret Thatcher in a hotel near London. Gerry Durkan, the prime suspect, is on the run in west London and Constable John Carlyle is drafted in to join the hunt to find him.
The increasingly frantic search exposes rivalries in the security services as up and coming MI5 agent Martin Palmer goes up against Special Branch veteran Mark Cahill. Palmer needs to find Durkan first, or see his embryonic career go into reverse. But the young spook has a dirty secret of his own, one that he will kill to keep.