There's something in Gaeta's tone of voice there, something Edgar can't put his finger on but he knows what it means: this is a guy who's used to dealing with people who might not want to talk about their past.

"Well," he says, his voice lowering too, and pauses for a moment.

"The Earth I came from froze over when I was a baby. Only life left on the planet was in this huge train, built to go all around the world and never stop. Folks who paid to get on the train, they were Front. Us who got on by lottery, we were Tail."