DS Tommy Murphy goes undercover in a convent when a young nun apparently commits suicide and a second vanishes. Posing as a priest, he finds any number of suspects. The older nuns obviously have a secret and are in league with a pharmaceutical firm. Murphy suspects they may be participating in illegal or unauthorized drug trials in their African mission. There is a young African novice who has regular nightmares and is clearly afraid of something. Then there is the gardener/handyman who also has secrets. When the missing nun is found dead, the police must move quickly before anyone else is killed.