The Scarlet Pimpernel by Baroness Emmuska Orczy
During the French Revolution a anonymous Englishman was helping the French aristocrats escape. Chauvelinis the French envoy to England. He is determined to catch The Scarlet Pimpernel. He threatens Marguerite Blakeney, the beautiful wife of Sir Percy Blakeney. If she doesn't help him catch the Pimpernel, he will arrest her brother for aiding him.
This was a fun book. It is very predictable though. I found it very enjoyable.