Catherine Vaughn, a top assassin from the 22nd century, is thrown into the past. She awakens beside the rumored frail Lord Sebastian Morgan, only to uncover his deadly secret—he's cunning, ruthless, and far from weak. Forced into a dangerous alliance, they navigate palace intrigue, battle enemies, and test each other's limits. But when Catherine seeks a truce, Sebastian grabs her hand and declares, "I'll marry you!"