The Pale Assassin by Patricia Elliott (Published by Hodder, July 2, 2009 in the UK and by Holiday House, November 15, 2009 in the US)
Eugenie de Boncoeur is growing up in Paris, unaware that her guardian has contracted her to marry the sinister spymaster known as 'le Fantome' when she turns sixteen. She finds herself falling for the handsome lawyer, Guy Deschamps, but there is little time for romance; France is descending into chaos as the Revolution takes hold. Soon Eugenie is fleeing for her life. Her brother Armand has become involved in a plot to save the King from the guillotine, the mob is searching for aristocrats, and le Fantome, the pale assassin, is on their trail - desperate for revenge.
I love historical fiction and the French Revolution is a great setting!! It sounds like this book will have a nice blend of history, romance, and adventure. I look forward to reading it!