Borrower of the Night is by Elizabeth Peters. The first book in the Vicky Bliss series. Vicky, art historian and college professor, finds a reference in a book that might lead to the discovery of a missing masterpiece by a famous German sculptor. Supposedly lost in the Middle Ages, it might actually be found in a castle in Rothenburg, Germany. Vicky and the colleague/boyfriend Tony set off on a race to find the altarpiece, but they are not the only ones seeking it. Not Amelia Peabody, but a fun read that will make you want to continue the series.
Ratings: 9th grade - 7 out of 10 - MP (mild profanity).