Weighed in the Balance — Anne Perry

When Countess Zorah Rostova asks London barrister Sir Oliver Rathbone to defend her against a charge of slander, he is astonished to find himself accepting. For, without a shred of evidence, the countess insists that the prince of her small German principality was murdered by his wife, the woman who was responsible for his exile twenty years before. Though private investigator William Monk and his friend Hester Latterly manage to establish that the prince was indeed murdered, as events unfold the likeliest suspect seems to be Countess Zorah herself....