The cause of death was totally unknown, but Max Brailovsky expressed a view that, highly unscientific though it was, not even Surgeon-Commander Katerina Rudenko attempted to refute.

'He couldn't live without Hal.'

Walter Curnow, of all people, added another thought.

'I wonder how Hal will take it?' he asked. 'Something out there must be monitoring all our broadcasts. Sooner or later, he'll know.'

And now Curnow was gone too – so were they all except little Zenia. He had not seen her for twenty years, but her card arrived punctually every Christmas. The last one was still pinned above his desk; it showed a troika laden with gifts speeding through the snows of a Russian winter, watched by extremely hungry-looking wolves.

Forty-five years! Sometimes it seemed only yesterday that Leonov had returned to Earth orbit, and the applause of all mankind. Yet it had been a curiously subdued applause, respectful but lacking genuine enthusiasm. The mission to Jupiter had been altogether too much of a success; it had opened a Pandora's box, the full contents of which had yet to be disclosed.

When the black monolith known as Tycho Magnetic Anomaly One had been excavated on the Moon, only a handful of men knew of its existence. Not until after Discovery's ill-fated voyage to Jupiter did the world learn that, four million years ago, another intelligence had passed through the Solar System, and left its calling card. The news was a revelation – but not a surprise; something of the sort had been expected for decades.

And it had all happened long before the human race existed. Although some mysterious accident had befallen Discovery out round Jupiter, there was no real evidence that it involved anything more than a shipboard malfunction. Although the philosophical consequences of TMA 1 were profound, for all practical purposes mankind was still alone in the Universe.