It's the last days of the Northern Ireland 'Troubles' in 1994. The British Government and the IRA are hurtling towards peace under international pressure, but both sides want one last attempt to win an outright victory.
Heading up the British unit is Mike Devon, their top undercover agent. He's up against Fergal McSweeney, the IRA's most notorious assassin. Both men clashed in an operation in Chicago ten years previously and both have the scars to show for it. A final showdown is inevitable.
The action swings relentlessly from Chicago to London, and from Glasgow to Belfast, as the three sides collide in a final bloody finale in the suburbs of Dublin.