A stunningly illustrated picture book full of mystery and suspense, from the bestselling author of The Storm Whale and Grandad's Island.“I know when the Grotlyn's been Slipping through your house unseen…”What is the mysterious Grotlyn? What sort of creature could it be, scuttling across the town, frightening everyone in its path? And why has it stolen PC Vickers' knickers?!A beautifully illustrated rhyming tale about things that go bump in the night for ages four and up, from picture book superstar, Benji Davies, winner of Oscar's First Book Prize 2014 and Sainsbury's Children's Book of the Year 2015. Perfect for fans of Oliver Jeffers and Jon Klassen.