An in-depth and detailed outline about the characters can be found in the study pack. However, here are the highlights for you.
Brother Cadfael is a monk in the Shrewsbury Abbey, but he has not always lived a pious life. In fact, he was just the opposite for many of his younger years, and even includes fighting in the crusades. Now, he charged with solving a mystery. His character is different from the usual medeval character in that he is very open minded toward the roles of women, doesn't always go along with religious traditions, and seems to be very wise.
Prior Robert of the Shrewsbury Abbey is Cadfael's boss. He is very enamored of his own authority and prestigue. It is this tendency that pushes him to try and acquire the relics for his church.
Sioned is a girl that lives in the village. She is in love with a boy that is forbidden to her because of his fugitive status. Her father arranges a marriage for her, which she refuses. When her father later dies, she, with the aid of Cadfael is able to be with her true love. She helps Cadfael solves the mystery.
Engelard is the young man that Sioned loves. He is a fugitive because he was caught poaching deer in a neighboring township. He works as an ox caller.