Tumbleglass - Kate Constable - Bog

"Thirteen-year-old Rowan is helping her older sister Ash paint her bedroom when she discovers a mysterious ring that transports them both back in time to 1999. To a party being held in the very same house! While Ash dances, Rowan unwittingly disrupts the laws of time, and when she wakes up back in the present day, her sister is missing and even worse, everyone in their family seems to be forgetting she ever existed. With the help of her magical neighbour Verity, Rowan must find the courage to travel back through the history of the house. But can she find everything she needs to rescue Ash before her sister disappears forever?"--Back cover