Actor Richard Johnson wrote the original story for this taut suspense drama that stars Rod Steiger as Niall Hennessy, a man who plans to blow up the British Parliament in retaliation for the accidental death of his family in Belfast. Johnson plays Scotland Yard-inspector Hollis, an expert in the struggles of Ireland, who under Commander Rice (Trevor Howard) attempts to locate Hennessy. Hennessy has journeyed to London with a plan to substitute himself for MP Burgess (Hugh Moxey) and, wiring himself up as a human bomb, to destroy the British power structure. In a twist, IRA leader Tobin (Eric Porter), realizing that the explosion will lead to more British repression on Northern Ireland, also travels to London to try to kill Hennessy before he can explode his bomb.