Scientist at Imperial College London regularly develop weapons to benefit the war effort and in 1943 they stumble across a gas that when inhaled produces indecisiveness of thought and action.

In fear of a second Battle of Britain when resources are depleted, Churchill authorizes a pre-emptive strike using the gas delivered by a single Lancaster bomber on key German airbases.

The bomber takes off but is shot down crash-landing in a lake somewhere inside the Home Counties in England, sinking without trace. Squadron Leader John Laine, the Excalibur pilot, returns at a seance soon after the crash to warn of the danger the gas brings, but his warnings go unheeded.

Over 40 years later the wreckage of the Excalibur is breaking up following local tremors and with it, the release of the gas. So begins a chain of events involving irrational behavior, even murder.

Detective Inspector Philip Graves is asked to investigate and in doing so, divert attention away from a certain retired Secretary of State, who as a young politician during the war ordered the Excalibur on its mission.