Seize the Wind by Heather Graham

Traveling through the forest north of London, Kate’s envoy is attacked by highwaymen, and Kate is kidnapped. The masked bandits’ leader is a man named Shadow, who is determined to use Kate as a ransom against the Duke of Manning.

When she tries to flee, Shadow imprisons her, and makes it clear that he’s in charge. But is her future with her bethrothed, a Duke she’s never met? Or here, with Shadow?