The story
A masquerade, a daughter, and a sister with the keepsakes.
Six years ago the lawyer Madeline met the heir Nicholas at a masked ball, and afterwards raised a clever daughter called Isla. Her half sister Vivienne stole the mementoes and used them to pass herself off as his lover, chasing the money and the standing. Then Madeline takes a job at Nicholas's group and they are in the same rooms again, with romance building through constant scheming and threats, until a rare hereditary disease and matching birthmarks say plainly what happened.