Sister Joan of the Order of the Daughters of Compassion has a habit of solving murders.

The sixth book in Veronica Black's popular mystery series, A Vow of Devotion finds the convent once again in turmoil just when it looked like things were getting back to normal. With Sister Theresa preparing for her initiation ceremony, two new postulants, a visiting hermit, and a caravan of New Age travelers in the area, there are plenty of suspects at hand after a sinister, batlike figure infiltrates the convent by night.

With a little help from the everagnostic Detective Sergeant Mill, Sister Joan once again finds herself the reluctant sleuth when she discovers first a knife, then a foreboding blood-red rose, and finally the bludgeoned body of a young novitiate—all within the walls of holy sanctuary.

Will the murderer kill again? One of the postulants knows more than she's telling, and Sister Joan, as usual, has pieced together more than she lets on. Balancing her vows to the Lord against her unerring investigative instincts, our detective-nun must find the killer before he strikes again.