The Mystery Girl.

Prince Sebastian of Lurania is forced to go into hiding when German forces invade his country. His niece, Countess Therese, is an ambulance driver with the French army. Her uncle requests that she meet him in a small town in Maine and bring the crown jewels with her. Unfortunately, a jewel thief finds out and makes a deal with the Luranian pretender to the throne: he will steal the jewels and he can keep them if he kidnaps and turns over the Countess to the usurper.