American intelligence agencies are fairly certain that it is being prepared for an underground reactor and reprocessing center, where nuclear waste is turned to bomb-grade plutonium.
They might try and organise a mass exit from the valley, or else storm the reprocessing centre.
And what if all this business up at the reprocessing centre turned out to be a damp squid?
Kent and Coyle were both invited to attend a crisis meeting at the reprocessing centre in an hour's time.
The Japanese are the last breeder-reactor customers for the European reprocessing centers.
"We're talking about late winter when the reprocessing center could be in operation."
A giant reprocessing center at Rokkasho in northeastern Japan is already a decade late, partly because of local protests.
Once the North Koreans allowed inspectors in, the atomic energy agency discovered a vast reprocessing center.
North Korea has denied any such reprocessing center exists and said that all of its nuclear sites are for civilian purposes.
The legislation also phases out the highly disputed shipment of nuclear waste to reprocessing centers in France and Britain.