Tracks (Mason Falls Mysteries) (Library Binding)
Nick and Ava have become friends over the fact that they're the only upper classmen who still ride the bus to school. And every day, they see the same boy--who they call The Kid--walking along the train tracks, even when the weather is terrible or when he's clearly fighting a bad cold.
When Nick notices the mysterious boy practically sprinting along the tracks one day and he doesn't show up the next, Nick and Ava begin to wonder if something might be wrong. But how can they help when they don't even know who The Kid is?