It's Christmas, and a local visiting dignitary suddenly takes ill immediately following his decision to bequeath his manorial estate to the abbey. Luckily, the abbey boasts the services of the herbalist Brother Cadfael, who hurries to the man's bedside, only to be confronted with two surprises: the man's wife is Richildis—whom Cadfael loved before he took his vows—and the poison is monk's-hood oil from Cadfael's stores. Using his knowledge of both herbs and the human heart, Cadfael deciphers a deadly recipe for murder.