Because Greyhald Spold knows that Death is looking for him, and has spent many years designing an impregnable hiding place.

He has just set the complicated clockwork of the lock and shut the lid, lying back in the knowledge that here at last is the perfect defence against the most ultimate of all his enemies, although as yet he has not considered the important part that airholes must play in an enterprise of this kind.

And right beside him, very close to his ear, a voice has just said: “DARK IN HERE, ISN’T IT?”