A small town is celebrating the millennium of the martyrdom of their patron saint, St Ceridwen (is there a real St Ceridwen?), and so a weeklong festival is planned, culminating in a play on the life of the saint, who, in addition to dying as a martyr, had defeated a dragon that plagued the small village, not my killing it, but by banishing it to a fen.
The Year 8 pupils of the BottomTop Middle School are given the responsibility of producing the play, and Felicity "Fliss" Morgan is chosen to play the part of St Ceridwen, while her best friend Lisa Watmough is one of four children playing the dragon, whose costume they create out of whatever materials they can find.
Lisa is at first reluctant to take part, as she has a strange feeling that something bad will happen, but once she gets started she participates enthusiastically, and it's Fliss's turn to get worried as Lisa seems to change, and not in a nice way, and those who are acting the dragon's part seem to become too enthusiastic. The tension increases, until the day of the festival itself.