His fingers found the lowest step. He pulled himself up, boots slithering on the smooth metal. The urge to breathe was rising fast, a balloon swelling painfully inside his chest. He kept climbing . . .

The ascent suddenly became easier as the ship tipped towards the horizontal once more. He increased his pace, opening his eyes. They stung, but he was clear of the gas. He took in more air and clambered into the throne room.

Gunshots rang through the ship. Not close – they were coming from the corridor with the armoury. What was happening – and where was Nina? He hurried to the broken window.

Pieces of ice fell past as he looked out, briefly disorientated; the whole cavern had changed, the once-sheer cliff now well off the vertical. This time, the berg had not rolled back to its original position. The water churned, the two moored boats tossed about like toys.

The Dionysius’s anchor swung towards the cliff – drawing his gaze to Nina. She was about halfway along the narrow ledge. Harhund and another man were ahead of her, the mercenary carrying the key behind. All clung to the ropes as the wall shuddered, so nobody could threaten her . . . but nor could she escape.

That meant the gunfire in the ship was being aimed at Cheng, Imka and Janco – no, just Cheng and Imka, he realised as he saw Vorster’s impaled body near Naider’s. He hurried up through the throne room. As long as Nina could hold on, she was safe – and Harhund’s employers wanted her alive.

Another burst made it clear that that didn’t apply to the rest of them. He snatched up some of his abandoned gear from beside the altar, then ran down the stairs.

Nobody was in the passage below. He pounded up it, following the sound of the gunfire.

‘Run, run!’ gasped Cheng as he passed the armoury. The towering suit leered demonically at him and Imka.

‘It’s a dead end!’ the South African protested.

‘There might be another way out – Mr Chase didn’t go all the way!’ But the young Chinese lacked confidence in his own words. He had gone upwards at the end of the entrance tunnel purely on instinct, the primitive urge to find higher ground when threatened. But now there was no turning back – a mercenary was pursuing them.

The corridor ahead started to descend, not as steeply as before. The ancient vessel seemed to be pulling itself upright, somehow dragging the enormous mass of the iceberg with it—

Bullets ricocheted from the walls behind them. Imka shrieked. They raced down the slope. The glow of the crystals meant there was no need for flashlights. Cheng saw the damaged end of the passage ahead – and also the exploded remains of the Dionysius’s crew.

He averted his eyes as he ran past. They were almost at the crushed section of corridor.

But Mr Chase had been right. No way out—