A Vow of Fidelity

Sister Joan of the Order of the Daughters of Compassion, seen before in Vow of Devotion, begins a somewhat far-fetched, seventh murder investigation outside the walls of her convent on the Cornish moors. Joan sets off for London and the 20th-year reunion with her art college classmates, hoping to promote the convent as a place for a quiet retreat and reflective seclusion--the institution's latest money-making endeavor. At Westminster Abbey, their prearranged meeting place, Joan learns that, within the last two years, two members of the class have died under suspicious circumstances; then she learns that a third was an apparent suicide only weeks before. As the surviving friends take advantage of the convent's retreat program, Joan begins to investigate and finds that one of her old classmates might be a murderer. Many of the familiar characters, including the usually fresh-witted Joan, have appeared in better light in earlier tales. Stretching credibility beyond its limits, this latest Sister Joan adventure is slack and disappointing. (Mar.)