Teen-aged postulate Therese is killed in a fire at the island convent, apparently caused by her smoking, the door to her room being locked from the inside. However, Poole suspects foul play when he finds that Therese has been sent a threatening note and clearly knew more than she should. Daryl Dexter, arranging public relations for the convent after the discovery of a holy well that cures the sick, is a prime suspect as Therese discovered he was bribing the 'sick' to claim they had been miraculously cured. Another suspect is Father John, guilty of an indiscretion many years ago at a convent where Therese eventually stayed. Poole uncovers a crime of passion in solving the case though he finds it harder to remove his phobia of nuns.