After sixteen-year-old Harriet Flynn trips over an ancient gravestone etched with strange markings in a seventeenth-century holiday village and reads the inscription, she and her friends are alarmed to wake up with supernatural powers.

Having magical abilities is fun at first, but when a series of accidents cause the group to become frightened, Harriet becomes determined to find out what's going on. While investigating the history of the gravestone they came across that night, Harriet realises she has unwittingly awakened a centuries-old, deadly curse and she is the only one who can put an end to it – and she has less than a day.

With time running out, Harriet must find the true magic key, to save herself and the ones she loves.