The Difficult Saint — Sharan Newman

After a harrowing stay with Catherine's in-laws in Scotland, Catherine LeVendeur and her husband, Edgar, have returned home with their two children to live a life of peace at last--or so they hope. But soon, Catherine's estranged younger sister, Agnes, returns to Paris with the news that she has been promised in marriage to a German lord. Bitter about their religious differences, Agnes wants no part of Catherine or Catherine's Father, Hubert--except for the sizable dowry that Hubert can provide. When Catherine and Hubert arrange for Agnes to be escorted to Germany with her dowry, they assume that they've seen the last of her.

But then one of Agnes's escorts returns to Paris with terrible news: Agnes's new husband appears to have been murdered by poisoning, and Agnes is the prime suspect. In spite of their differences, Catherine believes in her innocence, and knows that she must do everything she can to save her sister's life. And when Catherine and her brood travel to Germany to begin sleuthing in a dangerously anti-Semitic climate, it becomes clear that Catherine and Edgar's long-dreamt-of life of peace remains in the distant future--if they live to see it at all.