Eleven-year-old Bella Bright has just moved into Darkling House in Castleton. On her first day at her new school, she is spotted by a pair of manipulative mean girls, Skylar and Regan. They push her into inviting them to a Halloween sleepover. Another much friendlier girl, Lex, comes to Bella's rescue and offers to join the sleepover to support Bella, who is delighted to be making a real friend.

On Halloween night, things start getting spooky for the four girls, when the huge front door appears to shut itself, and their mobile phones lose signal. They decide to order pizza using the landline, but a hair-raising whisper comes down the line.

Skylar suggests they play hide and seek, but as she utters the words, the house appears to wobble and they discover all the exits are impossibly locked. Bella searches the manor and a ghostly teenage girl appears in front of her. She reveals herself to be Alice, a young girl who died in the house 150 years ago during a game of hide and seek gone terribly wrong. She has hidden Bella's three friends, and gives Bella a rhyming clue to find them in the enormous and cavernous house.

Bella has until midnight. After that, Alice will get to keep the girls as her playmates for ever...