While racing to intercept international assassin Sakov, who has arrived at the Greenways health clinic on the pretence of receiving therapeutic treatment, Unwin is unaware that the agent has designs on the new GK2 additive chemical that, mixed with water, produces a compound as combustible as high-octane fuel.

The sabotage of multiple military installations leads The Bishop to contact Unwin. Tracking down Brother Gregory, a vicar involved in a car accident near the site of the latest attack, Unwin helps Harding to slip into Brother Thomas' briefcase. Arriving at Pennydridge Seminary, Harding discovers that the vicars are in fact mercenaries who answer to their own Archdeacon.

Unwin and Harding are assigned to guard the King of Muldovia, who is in London to sign an oil rights treaty. The Muldovian Prince plots to overthrow the King, but his hitman's assassination attempt on the monarch is thwarted. The Prince instead conceals a bomb inside a toy bear intended for the King's son.