It was a good written historical romance, rather for young adults and chick-lit, with a little adventure (mystery). I have enjoyed it. 
 Nonetheless, I can't say I can't wait to read another book of series. I prefer more realistic historical romances. Here, there were too many too unrealistic scenes (e.g. a love scene on the boat in the Paris, or how they worked as spies). 
 The best part was a humor. It had a few really funny situations. But, when I want a witty historical romance, not necessary very realistic, I will pick Clare Darcy, Joan Smith, Marion Chesney or of course Georgette Heyer. As for this kind of adventure I will rather pick Emmuska Orczy or Patricia Veryan.