This is the second Veronica Black "Vow" mystery I've read, and I'd say that my problems with this book are similar to the ones I had with Vow of Sanctity -- that the final chapter consists of everything being suddenly "solved" -- lots of loose ends tied up, to make sure the reader has no unanswered questions about how it all fits together -- and a motive for murder that is not particularly credible.
However, getting to the last chapter is a lot of fun -- the book is well-written on the whole and moves right along. The characters are distinctive and although there are a lot, easy to keep track of (not one of those books where you have to take notes, maps, and charts). The convent setting interested me, and there was nothing so grizzly as to be upsetting to read (which is probably why this is considered a "cosy" mystery).
The plot involves a reunion of art students 20 years after a photograph was taken. They discover that some of the group are missing because they have died mysteriously. Sister Joan, our detective-heroine, smells a rat, and reluctantly gets drawn into looking into a possible connection between these deaths. The surviving students all end up at the convent on retreat (quite unbelievably), and Sister Joan has some concerns that she will be next on the killer's list -- if she can't discover who and why before the next killing.
All in all, a pleasant and engaging book, but not likely to be the kind of book you buy in hardbound and keep.