Meadowsweet

Original title: "The Brides of Friedberg".

Amid the royal splendor of the German court, vibrant young Trelawney Adair found that her secret attraction toward Prince Frederick, her sister's husband, had cast her inexplicably under a dark cloud of suspicion. Day by day her beautiful sister, Daisy, was growing mysteriously weaker, and gossip and innuendo about both Trelawney and Frederick were everywhere...

But only when bitter evidence of foul play and poisonous meadowsweet began to strike closer and closer did Trelawney realize that the sister she loved had been marked for death---and she herself maked as the perfect killer...