Some nuclear test explosions are seen. None go unnoticed: the planet registers every one, through the sea, the ground, the air. Thirty years ago, the world's nations agreed to stop testing, and to build something harder still: a system able to prove that agreement holds. THE ROAD TO ZERO traces that network of stations and laboratories from the negotiating rooms of the 1990s to some of the remote outposts where it stands today, in the words of the scientists and experts who keep it running, among them a facility in Chile reachable only by mule.