When twelve-year-old Kat Stephenson's family arrive in Bath to look for a suitor for her sister, it's not long before she realises the city is fizzing with wild magic. Stumbling on a plot to harness the magic in the Roman Baths, Kat finds that her brother is unwittingly involved. To foil the plot and save her brother, she must defy the Order of the Guardians and risk losing her new-found magical powers, forever.