Having run away from her family home to escape an arranged marriage, Welsh heiress Henry Nettleblack finds herself ambushed, robbed, and then saved by the mysterious Dallyangle Division - part detective agency, part neighbourhood watch. Desperate to hide from her older sisters, Henry disguises herself and enlists. But the Division soon finds itself under siege from a spate of crimes and must fight for its very survival. Assailed by strange feelings for her new colleague - the tomboyish, moody Septimus - Henry quickly sees that she's lost in a small rural town with surprisingly big problems.