Cross the charms of Brideshead Revisited with a contemporary financial thriller, and you'll come close to Thomas Caplan's refined, yet riveting novel, Grace and Favor. Overheard conversations are making American merchant banker John Brook suspicious of both his lovely British wife, Julia, and her blue-blooded but financially strapped family. Set mostly at the enormous country estate recently inherited by Julia's brother, the plot involves a risky business deal that could make them all rich -- if only treachery, murder, and financial ruin weren't waiting in the portrait-lined wings. Caplan builds conspiracy with the same exquisite, languorous sensibility that he uses to evoke the privileged setting. B+