The Devious Duchess (Regency Mystery/Romance‪)‬

Deirdre Gower refused to ruin her fiancé, Lord Belami, by marrying him--if her aunt proved to have murdered her brother. But the Duchess had brought the ancient Lord Dudley a bowl of stew, and he had succumbed to arsenic poisoning. The Duchess, Sir Nevil Ryder and who else wished to silence the old man before he could change his will? Regency Romance/Mystery by Joan Smith; originally published by Fawcett