Emily Feather and the Chest of Charms

the long version

"Emily Feather - the ordinary girl in an extraordinary family. Emily doesn't like the boy her older sister, Lory, keeps bringing home. There's something untrustworthy about him, though Emily can't put her finger on exactly what. Soon she discovers Lory is in danger! The boy has tricked her into taking him through the doors into the fairy world. Can Robin, Lark and Emily get Lory back? They must go through the attic, which Emily didn't even know existed, to sneak into the fairy world. Will they find Lory in time?" --Publisher's description.