Novelist April Poole reads her new book to Kerry Sarle, her publisher and sweetheart, and to Ronald Kenna, her editor. The story begins at a masked ball, where April meets Kerry and recognizes master thief Kenna. April retrieves a note discarded by Kenna and learns that he intends to steal the Mannister diamond. Meanwhile, the Earl of Mannister, hoping to end his daughter Diana's relationship with an impoverished American artist, orders her to deliver the jewel to her mannish female cousin, Clive Connal, in South Africa. Aboard the train, Diana persuades April to assume her identity. Eager to foil Kenna, April complies. When Kerry overhears a struggle in April's stateroom, he rushes in and ejects Kenna. In gratitude, April reveals her identity and mission. After Kerry receives a note from April that asks him to take the trunk to Clive, April disappears. Disconsolate, Kerry delivers the trunk. When Kenna and his cronies locate it, April springs out, pistol in hand, and captures them. As she concludes her tale, April embraces Kerry, who accepts the story.