Inspector Pascoe's grandmother dies, and he sets out to discover the truth about his grandfather: why he disappeared during WWI. Pascoe is falsely told that his grandfather was a deserter but continues his quest. An animal rights group, in a seemingly unrelated incident, attacks a pharmaceutical firm's labs. The leader (Amanda Marvell) escapes to the woods nearby and falls over a skeleton. Dalziel is attracted to Marvell but relentlessly sets out to solve the murder of her disciple, though her Jeep is involved. Flashbacks are used to show the threads linking the two cases. The skeleton is found to have arsenic in the bones; Marvell's brother's death in Africa is suspected not to be accidental; Dalziel discovers the theft of experimental data from the lab, showing it not to have a purely beneficent medical mission in Africa; and Pascoe proves his grandfather was innocent.