"She's my adoptive mum," says Matilda, then adds absently, "took me in when my biological parents ran off to Spain to escape the law. She was my teacher, but I'm not in school anymore. I was jumping up a class a week, and it got silly."

She's not quite a sufficiently oblivious five-year-old to fail to notice Charlie's face taking on much the same expression hers just got, only worse.

"Nobody we know knows where we are," she says, looking rather lost.

Everything else sort of follows logically from that.