Following 'A Vow of Silence' and 'A Vow of Chastity' Veronica Black's spirited sleuth, Sister Joan of the Order of the Daughters of compassion, reluctantly finds herself in another detective's dilemma.

This time, the Prioress, deciding Sister Joan needs a break from convent crime-solving, sends her on a spiritual retreat to a remote spot above a loch in Scotland where she can paint the local scenery—without signing her work, of course, to avoid the 'sin of singularity." But when, not long after her arrival, the venturesome nun rows out to an island to paint a monastery, she finds herself in a singular mess: Not only is someone following her, but she seems to be unearthing far too many secrets for her curiosity to handle.

Before she knows it, the good Sister finds herself exploring, by flickering candlelight, an ancient crypt where past Abbots rest. She discovers one skeleton too many. . . and it is wearing modern shoes. Forced against her intentions to contend with terrestrial puzzles, the intrepid Sister Joan, to the reader's perpetual delight, sets out to find the key to the loch's intriguing secrets.