Keith takes the train to attend the hell hole that is his private school, and though he’s used to the weirdos and creeps who frequent the locomotive, apparently not everyone aboard is.
There’s a stranger on this train that Keith can just tell is a target. Already a group of older men have set their sights on the boy, who’s not even aware of his surroundings, that’s how zoned-out he is.
So Keith, being the kind-hearted kid he is, takes it upon himself to lend his own defensive appearance to ward off creepers who may want to harm this oblivious boy, if only to keep the guy daydreaming peacefully.
He takes his job very seriously. This is his stranger after all.