'Happy to hear it, Oleg. Especially as I'm a hundred and three – as you know perfectly well.'

'Here we go again! Anyone would think you've never read Professor Rudenko's book.'

'Dear old Katerina! We'd planned a get-together on her hundredth birthday. I was so sorry she never made it – that's what comes of spending too much time on Earth.'

'Ironic, since she was the one who coined that famous slogan "Gravity is the bringer of old age."'

Dr Heywood Floyd stared thoughtfully at the ever-changing panorama of the beautiful planet, only six thousand kilometres away, on which he could never walk again. It was even more ironic that, through the most stupid accident of his life, he was still in excellent health when virtually all his old friends were dead.

He had been back on Earth only a week when, despite all the warnings and his own determination that nothing of the sort would ever happen to him, he had stepped off that second-storey balcony. (Yes, he had been celebrating: but he had earned it – he was a hero on the new world to which Leonov had returned.) The multiple fractures had led to complications, which could best be handled in the Pasteur Space Hospital.

That had been in 2015. And now – he could not really believe it, but there was the calendar on the wall – it was 2061.

For Heywood Floyd, the biological clock had not merely been slowed down by the one-sixth Earth gravity of the hospital; twice in his life it had actually been reversed. It was now generally believed – though some authorities disputed it – that hibernation did more than merely stop the ageing process; it encouraged rejuvenation. Floyd had actually become younger on his voyage to Jupiter and back.

'So you really think it's safe for me to go?'