It was the most harrowing sight he'd ever seen, but he fought back the shock and focused on a single thought: saving his family. All that mattered was that his wife and children survived.

It looked as though the wave had stopped.

Olsen watched for a while then picked his way carefully to the back of the house. The barrage of questions started right away. He looked into his children's wide, fearful eyes, and raised a hand to calm them, telling them it was over and they needn't be afraid. Of course it wasn't over – how could it be? But somehow they had to leave the house. He had the idea of escaping over the rooftops to dry land, but his wife said he'd been watching too much Hitchcock. How did he propose to do that with four kids? Olsen didn't know, so that settled it. He returned to his post by the window.

This time when he looked out he saw that the water was flowing back, racing towards the fjord and picking up speed.

We're going to make it, he thought.

He leaned out for a better view. At that moment the house shook violently. Olsen clung to the window. The floor was splintering. He wanted to leap back, but there was nothing beneath him. The living-room floor was a huge gaping hole. Water poured in and Olsen pitched forward. At first he thought he'd been jerked through the window, then he realised that the front of the house was hanging off the walls. It was tipping him into the water.

He screamed.

The people of Hawaii had lived with the monster for generations, and knew what would happen when it beat its retreat. The receding water created a violent pull that swept everything into the sea, washing over anything left standing. Those who had survived the first act of the catastrophe died in the second, but their death was filled with agony. Their end began with the futile fight for survival against the raging water, the struggle to swim against the tide. Their strength would give out and their muscles would weaken. They'd be struck by debris and their bones broken. They'd cling to anything they could find, only to be torn away again, swept onwards with the rubble and the mud.

The monster of the deep came on land to feed, and when it returned to the ocean it dragged its prey with it.

The first Olsen knew of that was when the front of the house tipped towards the maelstrom. Then he knew he was going to die. As the wall tilted further, more explosions rang out across the harbour as the remains of ships and oil plants burst into flames. Almost every electrical system in the city had failed as one short-circuit triggered the next. Maybe that was how he would be killed – by the high-voltage current in the water.

He thought of his family. For a split second he thought of Sigur Johanson, and was seized with impotent rage. Johanson was to blame. He'd kept something back – something that might have saved them, the son-of-a-bitch.

With a deafening crash the facade of the house smashed down on a tree that was straining in the water. Olsen was catapulted head-first through the window. He clutched at the air and grasped leaves. A stream of mud raged beneath him. He dangled from the branch, as it swung madly up and down, then tried to pull himself up. Fragments of wood and plaster rained down on him from above, narrowly missing his head. The jet of water ripped chunks out of the timber wall. The front of his house warped, splintered and tore apart He tried to move closer to the trunk. Lower down, and a little to one side, there was a thicker branch that he could reach. Maybe he could rest his feet on it. The huge tree groaned, and he made his way forward, hand over hand, gasping for breath.

The remains of the wall crashed into the water, tearing branches and foliage as it fell. Olsen's branch jerked up. His fingers uncurled. Suddenly he was hanging from one arm. If he fell, his fate would be sealed. He turned his head awkwardly for a glimpse of his house – or whatever remained of it. Please, he thought, don't let them be dead.

The house was still standing.

And then he saw his wife.

She'd crawled to the edge and was on her hands and knees, staring out at him. There was a look of determination on her face, as if she was about to dive into the water to help him. She couldn't, of course, but she was there, and she was calling to him. Her voice sounded firm, almost angry, as though he should stop messing around because everyone was waiting.

For a moment Olsen just looked at her.

Then he tensed his muscles. His free hand stretched up and grabbed the branch. He dug his fingers into the wood and began to move forward until his feet were directly above the sturdy branch. Slowly he let himself down. Now he could balance properly. He stood up. His shoulders quivered. He wrapped his arms round the trunk, pushing his face against the bark and staring at his wife.

It took forever. The tree stayed put, and so did the house.

When the water had finally dragged its booty into the sea, he was able to climb down shakily into the wasteland of debris and mud. He helped his wife and children to leave the house. They took only what they needed: money, credit cards, passports, and a few bits and pieces of sentimental value, hastily crammed into a couple of rucksacks. Olsen's car had disappeared. They'd have to walk, but anything was better than staying put.

Silently they left the ruins of their home and walked along the other side of the river, away from Trondheim.

Cataclysm

The wave kept spreading outwards. It flooded the east coast of the UK and the west coast of Denmark. Between Edinburgh and Copenhagen the shelf was unusually shallow. Dogger Bank loomed up from the seabed, a relic of the time when the North Sea was still partly dry land. It had once been an island, its shores home to numerous animals that crowded together as the tides kept rising, until eventually they drowned. Now it lay thirteen metres below sea level, and it forced the surging wave to rear higher.

South of Dogger Bank the shelf was crammed with the oil platforms that lined the south-east coast of Britain, the northern shores of Belgium and the Netherlands. The wave raged more ferociously than it had further north, but the uneven surface of the shelf, with its sand bars, ridges and chasms, acted as a brake. The Frisian Islands were inundated, but the wave lost some of its momentum so Holland, Belgium and northern Germany were spared its full force. By the time it reached The Hague and Amsterdam, its speed had dropped to a hundred kilometres per hour, which was still enough to destroy large sections of coastline. Hamburg and Bremen lay further inland, but the mouths of the Elbe and the Weser were as good as unprotected. The tsunami raced along the rivers, flooding the surrounding area before it reached the cities. In London the Thames rose sharply, breaking its banks and smashing ships into bridges.

The surging water spilled into the Strait of Dover, shaking the coastline to Normandy and Brittany. Only the Baltic emerged unscathed. The water off the coast of Copenhagen, Kiel and the other Baltic cities was choppier than usual, but the tsunami didn't reach them, shuttling between the Skagerrak and Kattegat until it collapsed. Further north the devastation continued unabated as the tsunami slammed into the shores of Iceland, Greenland and Spitsbergen.

After the disaster, the Olsens had headed straight for higher ground. Later on, when Knut Olsen thought about it, he couldn't say why. He was the one who'd suggested it. Maybe he dimly recalled a film he'd seen about tsunamis or an article he'd read, or maybe it had been intuition. Either way, the decision to flee had saved their lives.

Most people who survived the coming and going of a tsunami were killed all the same. When the first wave was over, they returned to their villages and houses to see what remained. But a tsunami was made up of a succession of waves. The large intervals between peaks meant that the second wave hit when people thought they were safe.