They worked in teams of a hundred, at first. They were driven to extremes of heat and cold, hunger and exhaustion. They were woken in the middle of the night, left stranded on the dark side of asteroids with only a few hours to reach safety. They trekked across hi-grav jungle worlds that sucked them deep into the ­putrid mud. Each night they pulled off their boots and removed bloated leeches from their skin. They staged mock attacks on polar defence silos, trudging across ice plains and glaciers that creaked and groaned like tortured beasts.

Their instructors drove them incessantly. Over the three years of training their numbers were steadily whittled down through dismissal, execution and accident, until they numbered only a few thousand.

Yedrin was sure it was a hell that would never end, but one morning after yet another trooper had dropped out, their trainer, a no-nonsense Cadian named Larsk, suddenly walked in as they were shovelling down their brief morning meal. ‘Congratulations,’ he said. ‘You have passed the initial training. Finish your breakfast. Pack your bags. We’re moving out at oh-eight-hundred hours.’

Larsk started to walk away. It was Yedrin who put his hand up. ‘Sir, what do we do between now and then?’

They had never seen Larsk smile, but he did now. ‘You get some rest. You’ll need it. This afternoon we’re moving into phase two of the training.’

Phase two proved to be much like the first, only the tasks and challenges set for them were harder. The training intensified yet again, and Larsk came to look like a doting uncle by comparison.

The one benefit, Yedrin noted, was that the chaff had been winnowed out. There was a sense of achievement in just getting this far and knowing everyone about you had done the same. In crossing the featureless plains of El’Phanor, building rope bridges across the fissures, or a night drop in the ice and snow of Yuddson’s Glacier, you could rely on the grit and knowledge and determination of the other cadets as you clawed an ice-cave till your bare hands stained the snow red with blood.

Failure became less commonplace. They worked as teams to carry each other through the hardest challenges; it was the only way of getting through alive. Powerful personal bonds made each squad stronger than ten individuals.

By the time they returned to their base camp, nearly a year after their initial induction, another intake of fresh-faced recruits had arrived, a thousand strong, parading to hear the same kind of speech.

Yedrin looked at the newcomers as if they were another species. Only then did he realise the transformation that had been done to him. He was separate now. His mind knew calm and focus and the power of decision. His body was lean and tireless. There was only one thing left: phase three.