The Cabochon Emerald — Elizabeth Hawksley

There is a fortune at stake. The cabochon emerald, heirloom of the de Cardonnels, has disappeared in the chaos of the French Revolution. The young Anna de Cardonnel, fleeing from the terror, finds herself in London, living with her English relations. Then a mysterious stranger arrives as a suitor: but is Laurence Redbourn all he seems? Could he possibly have got wind of the missing emerald? And what of his brother, Luke, a respectable city businessman? Both profess an interest in Anna, and one of them will stop at nothing...