Someone's been spying on the Harlowe family. Who? That would be Joseph Leman, the guy we barely hear about until Lovelace makes him Accessory #1 to Clarissa's departure slash abduction.
Actually, it seems like it would be pretty fun to be Leman. He gets to make a ruckus with guns in the courtyard to distract the Harlowes, but he never seems to get blamed. Oh, and he accidentally spills the beans about Lovelace's location to Colonel Morden, but he gets off scot-free. It's jolly good fun to play at being a secret spy when none of the drama concerns you, what ho.