I believe you're referring to the Sister Joan Mysteries by Veronica Black. They all begin with the title "A Vow of...."
Christine B | 02.29.08 - 3:59 pm | #

Yup -- good series! There are about a dozen books, I think.
'thann | 02.29.08 - 9:55 pm | #

You might also try the Brother Cadfael seriesby Ellis Peters.
KevinK | 02.29.08 - 11:11 pm | #

That's exactly it! Thank you very much for your help, and thank you, Mark, for posting my question.

Shea readers = the new Google
Darren Jones | 03.03.08 - 12:25 pm | #