Dylan is the only boy living in the tiny Welsh town of Manod. His parents run the Snowdonia Oasis Auto Marvel garage - and when he's not trying to persuade his sisters to play football, Dylan is in charge of the petrol log. And that means he gets to keep track of everyone coming in and out of Manod - what car they drive, what they're called, even their favourite flavour of crisps. But when a mysterious convoy of lorries trundles up the misty mountainside towards an old, disused mine, even Dylan is confounded. Who are these people - and what have they got to hide?