Newly arrived in London for a season under her aunt's patronage, Kathryn St. David is surprised with a ball--and with meeting dashing Nigel Moorhaven, Marquis of Blackshire. When her aunt loses a diary containing scandalous secrets, she sends Kathryn to a girls school to find it. There, Kathryn meets up with Nigel--an operative known as the Blue Devil--and a mystery with mistaken identities unravels.