Diana Wynne Jones 
Eight Days of Luke 

There seemed nothing odd about Luke to begin with – except perhaps the snakes. If they were snakes, that is… David wasn’t sure."Just kindle a flame and I’ll be with you, " says Luke. David thinks he’s joking, but certainly, whenever he strikes a match, Luke appears immediately.But David’s new friend seems to have some extraordinary friends and relations, and some very dark secrets. And when David enters into a bargain with the mysterious one-eyed Mr Wedding, life gets very hot indeed!