The sisters face a demon named Abraxas , who steals the Book of Shadows and undoes some of the spells they've cast (in reverse order), releasing old vanquished enemies of the Charmed Ones and forcing them to remember the vanquishing spells from memory alone. The sisters have one chance to recapture the Book of Shadows or they will lose their powers forever. The sisters also meet their new neighbors, Jenny and her uncle Dan Gordon . Phoebe and Piper learn through the Wiccan community that because their anniversary of activating their inherent powers falls on an equinox , a wiccan holy day , each of their powers will be more developed and greatly magnified but only temporarily.