A boy called Theo was staying over at a friend's house. Late at night, going to the bathroom, he noticed a faint grey haze in the hallway and a smell like something burning. A thin line of smoke was creeping out from under the kitchen door downstairs. Everyone else was asleep. The house was quiet and dark. Theo's first thought was that he might be imagining it, and that waking the whole house would be so embarrassing if he was wrong.