After surviving an attempt on his life, Bognor strikes up a friendship with an unusual monk called Xavier. Meanwhile, the local madman, Batty Tom informs him he might have seen the murderer.
After his colleague Collingdale is killed hunting for a double agent selling British agricultural formulas to the Russians, Bognor is sent to replace him.
Even after solving the mysteries of the running monk and the locked backroom, Bognor's troubles are not over, especially after Batty Tom's father, Lord Collingwood, shows up and blows his cover.
Bognor is suspicious when he learns that one of the monastery's regular visitors, a schoolmaster called Jones, is actually the high-level civil servant Graymer Burton.
Batty Tom turns up dead and so does a letter supposedly written by him in which he confesses to the murder of Collingdale. Bognor is not convinced especially after noticing suspicious goings-on in a mysterious locked room in the shed.
While nursing a nasty bruise, Bognor has to find his nightly assailant, find the clue in an ominous poem, and deal with a suspicious journalistic union official.
