Prince Karl is in love with her and intends to force her into a morganatic marriage.

Otherwise she is safe.

The American, John Scott, in addition to his duties as a spy for France, a country that he loves and admires, intends, if human endeavor can achieve it, to rescue Mademoiselle Lannes and bring her back to Paris." Delaunois took one hand from the steering rudder and turned glistening eyes upon John.
"It's a knightly adventure," he said.

"It will appeal to Frenchmen when they hear of it, and yet more to Frenchwomen.

I should like to shake the hand of this American, John Scott, and since he is not here, I will, if you will let me, shake the hand of his nearest French relative, Jean Castel." He opened his gloved palm and John's met it in a strong grasp.
"I'm glad," said Delaunois, "that I saw you, and that I am able to give you this lift.