Whatever the truth, no-one could seriously imagine that, more than two centuries after his death, the legend of the great Zulu tyrant would cast its shadow across worlds he never knew.

During the decade after the ignition of Jupiter, and the spreading of the Great Thaw across its satellite system, Europa had been left strictly alone. Then the Chinese had made a swift flyby, probing the clouds with radar in an attempt to locate the wreck of the Tsien. They had been unsuccessful, but their maps of dayside were the first to show the new continents now emerging as the ice-cover melted.

They had also discovered a perfectly straight two-kilometre-long feature which looked so artificial that it was christened the Great Wall. Because of its shape and size it was assumed to be the Monolith -or a monolith, since millions had been replicated in the hours before the creation of Lucifer.

However, there had been no reaction, or any hint of an intelligent signal, from below the steadily thickening clouds. So a few years later, survey satellites were placed in permanent orbit, and high-altitude balloons were dropped into the atmosphere to study its wind patterns. Terrestrial meteorologists found these of absorbing interest, because Europa – with a central ocean, and a sun that never set – presented a beautifully simplified model for their text-books.

So had begun the game of 'Europan Roulette', as the administrators were fond of calling it whenever the scientists proposed getting closer to the satellite.

After fifty uneventful years, it had become somewhat boring. Captain Laplace hoped it would remain that way, and had required considerable reassurance from Dr Anderson.

'Personally,' he had told the scientist, 'I would regard it as a slightly unfriendly act, to have a ton of armour-piercing hardware dropped on me at a thousand kilometres an hour. I'm quite surprised the World Council gave you permission.'

Dr Anderson was also a little surprised, though he might not have been had he known that the project was the last item on a long agenda of a Science SubCommittee late on a Friday afternoon. Of such trifles history is made.

'I agree, Captain. But we are operating under very strict limitations, and there's no possibility of interfering with the – ah – Europans, whoever they are. We're aiming at a target five kilometres above sea level.'

'So I understand. What's so interesting about Mount Zeus?'

'It's a total mystery. It wasn't even there, only a few years ago. So you can understand why it drives the geologists crazy.'

'And your gadget will analyse it when it goes in.'

'Exactly. And – I really shouldn't be telling you this – but I've been asked to keep the results confidential, and to send them back to Earth encrypted. Obviously, someone's on the track of a major discovery, and wants to make quite sure they're not beaten to a publication. Would you believe that scientists could be so petty?'

Captain Laplace could well believe it, but did not want to disillusion his passenger. Dr Anderson seemed touchingly naïve; whatever was going on – and the Captain was now quite certain there was much more to this mission than met the eye – Anderson knew nothing about it.

'I can only hope, Doctor, that the Europans don't go in for mountain climbing. I'd hate to interrupt any attempt to put a flag on their local Everest.'

There was a feeling of unusual excitement aboard Galaxy when the penetrometer was launched – and even the inevitable jokes were muted. During the two hours of the probe's long fall towards Europa, virtually every member of the crew found some perfectly legitimate excuse to visit the bridge and watch the guidance operation. Fifteen minutes before impact, Captain Laplace declared it out of bounds to all visitors, except the ship's new steward Rosie; without her endless supply of squeezebulbs full of excellent coffee, the operation could not have continued.

Everything went perfectly. Soon after atmospheric entry, the air-brakes were deployed, slowing the penetrometer to an acceptable impact velocity. The radar image of the target – featureless, with no indication of scale – grew steadily on the screen. At minus one second, all the recorders switched automatically to high speed...

But there was nothing to record. 'Now I know,' said Dr Anderson sadly, 'just how they felt at the Jet Propulsion Lab, when those first Rangers crashed into the Moon – with their cameras blind.'

Only time is universal; night and day are merely quaint local customs, found on those planets which tidal forces have not yet robbed of their rotation. But however far they travel from their native world, human beings can never escape the diurnal rhythm, set ages ago by its cycle of light and darkness.

So at 01.05, Universal Time, Second Officer Chang was alone on the bridge, while the ship was sleeping around him. There was no real need for him to be awake either, since Galaxy's electronic senses would detect any malfunction far sooner than he could possibly do. But a century of cybernetics had proved that human beings were still slightly better than machines at dealing with the unexpected; and sooner or later, the unexpected always happened.

'Where's my coffee?' thought Chang grumpily. 'It's not like Rosie to be late.' He wondered if the steward had been affected by the same malaise that had overtaken both scientists and space crew, after the disasters of the last twenty-four hours.

Following the failure of the first penetrometer, there had been a hasty conference to decide the next step. One unit was left; it had been intended for Callisto, but it could be used just as easily here.

'And anyway,' Dr Anderson had argued, 'we've landed on Callisto – there's nothing there except assorted varieties of cracked ice.'

There had been no disagreement. After a twelve-hour delay for modification and testing, Pen No. 3 was launched into the Europan cloudscape, following the invisible track of its precursor.

This time, the ship's recorders did get some data – for about half a millisecond. The accelerometer on the probe, which was calibrated to operate up to 20,000 gee, gave one brief pulse before going off-scale. Everything must have been destroyed in very much less than the twinkling of an eye.

After a second, and even gloomier, post-mortem, it was decided to report to Earth, and wait in high orbit round Europa for any further instructions, before proceeding to Callisto and the outer moons,

'Sorry to be late, Sir,' said Rose McCullen (one would never guess from her name that she was slightly darker than the coffee she was carrying) 'but I must have set the alarm wrong.'

'Lucky for us,' chuckled the Officer of the Watch, 'that you're not running the ship.'

'I don't understand how anyone could run it,' answered Rose. 'It all looks so complicated.'

'Oh, it's not as bad as it looks,' said Chang. 'And don't they give you basic space theory in your training course?'

'Er – yes. But I never understood much of it. Orbits and all that nonsense.'

Second Officer Chang was bored, and felt it would be a kindness to enlighten his audience. And although Rose was not exactly his type, she was undoubtedly attractive; a little effort now might be a worthwhile investment. It never occurred to him that, having performed her duty, Rose might like to go back to sleep.

Twenty minutes later, Second Officer Chang waved at the navigation console and concluded expansively: 'So you see, it's really almost automatic. You only have to punch in a few numbers and the ship takes care of the rest.'

Rose seemed to be getting tired; she kept looking at her watch.