When Crazy Jack Staple, lately of Wellington's returns to civilian life after the defeat of Napoleon, he finds that there's not much to satisfy the adrenaline junkie he's become, and no woman who really interests him. Then, while escaping from his boring cousin's boring houseparty he rides into Derbyshire to visit a friend and puts up for the night at a lonely toll gate cottage when he finds the gate-keeper has left his ten year old son, Ben, alone and petrified.
Jack not only finds a mystery, but he finds romance in the shape of Nell, granddaughter of the ailing squire, competent and capable, and somewhat too tall for polite society and the 'ton.' It's love at first sight for Jack, but since he's masquerading as the gatekeeper's cousin, Nell takes a bit of convincing, however her retainers (faithful groom and nurse/companion) have no qualms about Jack and quickly decide that he's Nell's likely saviour as she'll soon be ousted from her home when her grandfather dies (as he has left it to her the obvious male heir, her unsympathetic cousin).
At its heart this is as much mystery as romance. The keeper, Ben's father, only stepped out for an hour, but now he's missing. Nell's odious cousin and his even more odious friend have installed themselves in the manor which the cousin hopes soon to inherit, but they don't seem to have a very good reason for doing so. There's a good-hearted highwayman and a Bow Street Runner sniffing around.
Jack latches on to the mystery, determined to solve it and so the romance almost takes a back seat until romance and mystery collide. There's much more derring-do than in Heyer's usual Regency Romances and it fairly bounds along to a pistols and fisticuffs conclusion.