The Precious Parcel (1916)

The story deals with a young man who performs an unusual service for Great Britain under the auspices of "The Younger Sons," an organization of the younger sons of British nobles. He is ordered to marry an American girl, because by so doing he automatically annuls an old grant of hers to a throne in Canada. His instructions are to open a packet on a certain day, and when he does, just after his marriage, he learns that unwittingly he has carried out his orders.