A man named Colin delivers money to an unknown destination in Belfast, taking some of the cash in the process. The recipients realize that money is missing but are then attacked. Soon afterwards, the delivery driver is kidnapped and killed at the same time as Colin is murdered whilst swimming.
Harold Shand, a London gangster, is aspiring to become a legitimate businessman and is trying to form a partnership with the American Mafia, with a plan to redevelop London Docklands. Shand's world is suddenly destabilized by a series of unexplained murders and bomb attacks. He and his henchmen try to uncover his attackers' identities whilst simultaneously trying not to worry their visitors, fearing the Americans will abandon him if they think he's not in full control. Harold's girlfriend, Victoria, tells the Mafia representatives Shand is under attack from an unknown enemy, but assures them Shand is working to quickly resolve the crisis. She starts to suspect Harold's right hand man, Jeff, knows more about who is behind the attacks than he claims.
After some investigation, Harold confronts Jeff who confesses he sent Harold's friend Colin to Belfast to deliver money raised by Irish Navvies to the IRA. He explains that three of the IRA's top men were killed on the same night after discovering some of the money had been stolen. Harold realizes the IRA have come to the conclusion that he sold them out to the security forces and pocketed the missing cash for himself. Vowing to destroy the terrorist organisation in London, Harold loses his temper and kills Jeff in a frenzy.
Harold sets up a meeting with the IRA's London leadership. He ostensibly offers them £60,000 in return for a ceasefire but double crosses them and has them shot as they are counting the cash. Believing his enemies are dead, Harold travels to the Savoy Hotel to triumphantly inform his Mafia partners only to find the Americans preparing to leave, having been spooked by the carnage. In response to their derisory comments about the UK, Harold berates them for their arrogance and dismisses them as cowards.
Leaving the hotel, Shand steps into his chauffeur-driven car only to find it has been commandeered by IRA assassins. As the car speeds to an unknown destination, Shand contemplates the inevitability of his fate.
