Longlisted for the Carnegie Medal for WritingCassie-s older brother Byron has fallen in with the wrong crowd - it-s soon clear these boys are wild, reckless and not human at all. They are tylwyth teg - Fair Folk, who tempt humans down into the dark places of the world. And Byron is tempted. When he goes missing, Cassie and her cousin, Si- follow his trail to an old abandoned railway tunnel which goes down and down into Annwn, the underworld. Here they find that the tylwyth teg are restless - and angry. Their leader, Gwenhidw, wants to protect Annwn from the damage humans are doing to the world. Byron is part of her plan. But Cassie won-t let her big brother be part of anyone-s plan. Can she rescue her brother before it is too late?
