All 17-year-old Daphne Reynolds (AMANDA BYNES) has ever wanted in her life is a father, but her wedding-singer mother, Libby (KELLY PRESTON), has yet to find a soul mate like Henry Dashwood (COLIN FIRTH). The two met seventeen years earlier in Morocco where they were unofficially married, but when she returned with him to his aristocratic home, her bohemian style didn't sit well with the rest of the family including their royal advisor, Alastair Payne (JONATHAN PRYCE). Accordingly, she moved back to America without letting Henry know she was pregnant.
Feeling that half of her is missing, Daphne sets out for London to introduce herself to her dad, unaware that he recently stepped down from the House of Lords and is running for Parliament as a commoner. Nor does she know that he's about to marry Alastair's haughty daughter, Glynnis (ANNA CHANCELLOR) and thus become stepfather to her snooty teenage offspring, Clarissa (CHRISTINA COLE).
With the help of local musician Ian Wallace (OLIVER JAMES), Daphne gets acclimated to her surroundings and then sneaks into the Dashwood estate where she meets Henry, his widowed mother, Lady Jocelyn (EILEEN ATKINS), and everyone else. Since Daphne's sudden presence provides ample opportunity for unwelcome controversy and a likely scandal, Alastair and his brood deem that they should get rid of her as soon as possible.
Yet, Henry feels that he must get to know his biological daughter. As he begins to loosen up and Daphne eventually tries to fit into their prim and proper lifestyle, the two must decide whether to be true to their real selves, all while dealing with the pending election as well as the efforts of Glynnis and Clarissa to drive Daphne away.