"Hello Earth! Hello London!"

But no reply was forthcoming to the message sent out by the spaceship in which the four pioneers had been exploring all the planets en route to Pluto, and which was now on its way back to London after two long years. Even the silence failed to dismay the voyagers; it could well be explained by a major fault of the airport's wireless transmitter. It was only when they touched down that they realised some terrible catastrophe had hit Earth in their absence...