Ten-year-old Sly is spending the weekend with their fortune-telling grandmother at the mysterious Madsen Mansion.

It's Samhain, a time when the spirits can cross over into the living world, and the old mansion has secrets whispering in the rafters and unused rooms. When Sly and their grandmother hear a voice calling, Sly unlocks a cabinet that reveals a ghost girl who is trapped in a mirror. Then they accidentally speak the words of the spell that enchanted the girl in the first place, and Sly and their grandmother risk being imprisoned in the mirror as well. With the clock ticking till the end of Samhain, it's up to Sly to solve the ghost's riddles and puzzles and locate a long-lost book of spells in hopes of freeing them all.