One moment, Isla Crawford is inside McQuivey's Costume Shop trying on a Jacobean-style gown for the parliamentary Autumn Ball, and the next, she is standing in an unfamiliar garden, barefoot, coatless, and at the mercy of a fierce storm. Confused, she seeks refuge in a Tudor manor, where she discovers that she has inexplicably traveled back to 1605, mere weeks before the culmination of Guy Fawkes's infamous Gunpowder Plot.

Simon Hartworth, Lord Bancroft, finds his orderly seventeenth-century life disrupted when a mysterious woman appears on his sister's doorstep during a storm. Intrigued by the stranger's quirks and bewildering speech, he feels compelled to protect her and heed her warnings about a fatal plot against Parliament. As Simon is drawn into Isla's dangerous scheme to stop the evildoers, he can't help but also feel drawn to her.

With seemingly no way to get back home, Isla uses her twenty-first-century knowledge of the past to try to thwart Guy Fawkes and his coconspirators without altering the course of history forever. She and Simon must race to unravel the threads of the treasonous plot even as they wonder how their hearts will navigate their deepening connection and the seemingly insurmountable four centuries that separate their lives.