Everbody likes Mr Mahli, especially his neighbours,nine-year-old Tomos and Alys. When he goes on holiday they look after his garden on Cwmdonkin Drive in Swansea for him. But they are not allowed in his mysteriously empty shed. But the friends soon find out the ordinary-looking shed is far from empty - it is home to an odd, slightly grumpy ghost called Dylan. Dylan soon persuades the children to take him to school with them for a change of scenery - at first he behaves, but then things start to get out of hand.
