James Montgomery has inherited his father's meager, run-down estate, his debts, and the care of his mother and two sisters. With no other ideas to solve the problem of providing for his family, he decides to take employment: He will escort the unthinkably rich Maidenhall heiress to her future husband. Jamie is (not surprisingly) a very handsome guy, and together with his sisters decides that the only way to get out of their dilemma is to elope with the heiress in the hope of getting access to her riches...But Axia, the wild heiress, has no mind for her arranged marriage. Having never experienced it, she is determined to have a taste of freedom on her trip across England to her future husband. She offers her poor but beautiful (and mean and vain) cousin Frances the chance to be heiress for 2 weeks - they will trade places for the duration of the trip, to give Axia some fun before her marriage.
So when Jamie arrives to escort the heiress, he not only mistakes Frances for the heiress, but unfortunately tries to enlist the seemingly poor Axia to help win her over - he basically tells her about his fortune-hunting plans. The two get off on a very bad start, but after an accidental sexual encounter Axia starts to think better of him, whilst Jamie starts to look twice at Frances's 'poor', feisty cousin - all whilst Frances is scheming to trick Jamie into a marriage with a girl whom he thinks is the heiress.