Never get into cars with strangers. It's one of the first things children learn.

But Jim's not really a stranger, is he? He doesn't seem to hide much of himself at all (at least, not that Richard's noticed; what he's seen from Jim more or less matches up with what he's seen on the BBC DVDs, at least). But he is something else entirely.

"Er. OK," he says, getting up slowly and slinging his knapsack over one shoulder. "Where are we going?"

All the same, he starts following before Jim even answers.