The whale hit the Lady Wexham with such force that the vessel rocked violently. There was a cracking, splintering sound. The whale dived down, and people on the top deck were thrown to the floor. The sea around the craft foamed and boiled, then several humpbacks rose to the surface. Two dark bodies launched themselves into the air and hurled themselves at the hull.

'Vengeance!' shrieked Greywolf. There was a hysterical edge to his voice.

The Lady Wexham was twenty-two metres long, far longer than any humpback whale. She had a permit from the Ministry of Transport and conformed to the Canadian Coast Guard's safety standards, which required passenger vessels to be able to withstand rough seas, metre-high breakers and the occasional collision with a lethargic whale. The Lady Wexham had been designed to cope with all such misfortunes. But she hadn't been designed to contend with an attack.

From across the water Anawak heard her engines start. Pandemonium broke out on the two viewing decks, and screams of terror echoed over the waves. People were pushing past each other in blind panic. The Lady Wexham started to move, but a whale rose out of the water, catapulting itself against the bridge. Even this assault wasn't enough to capsize her, but now she was pitching dangerously, as debris rained into the water.

Anawak knew he had to do something. Maybe he could distract the whales. His hand reached for the throttle.

At that moment another scream pierced the air, but this time it was coming from behind him. Anawak spun round.

He was just in time to see the body of an enormous humpback surge vertically out of the water, looking almost weightless. It rose, ten, twelve metres into the air and, for a heartbeat it hung above the little red motorboat with the three protestors.

Anawak had never seen anything so terrifying, and yet so beautiful at such close range.

'Oh dear God no,' he whispered.

As if in slow motion the body gently tipped and started falling. A shadow descended on the little red motorboat, then swallowed the Blue Shark's bow. It grew longer and longer as the enormous body plummeted downwards, travelling faster by the second…

Anawak jammed down the throttle. Greywolf's boat was also quick off the mark – heading straight for Anawak. The two boats collided and Greywolf's driver disappeared overboard but Anawak didn't stop. Before his eyes, thirty tonnes of humpback crashed on to the motorboat, burying it and its crew in the water, and hitting the front of the Blue Shark. The Zodiac's stern flipped up at right-angles to the water, sending its load of orange-clad passengers spinning through the spray.

It was a chilling sight. 'The campaigners' boat had been reduced to splinters and the Blue Shark was drifting upside-down. The water was full of people, shouting and paddling wildly. Their orange suits had inflated automatically to keep them afloat but some lay still on the water, killed by the weight of the whale. Across the waves, the Lady Wexham was surrounded by flukes and fins. He watched as she picked up speed, listing severely.

Anawak picked his way slowly through the drifting bodies, trying to avoid causing more injuries. He flipped on to channel 98 and reported his position. 'We're in trouble,' he barked. 'Casualties and maybe fatalities.' Every boat in the area would pick up his distress signal. He didn't have time to say more or to explain what had happened – there'd been a dozen or so passengers on the Blue Shark, plus Stringer and her deputy, then the three protestors in the motorboat, seventeen in all.

'Leon!' Stringer was swimming towards him. Anawak grabbed her hand and pulled her aboard, then spotted dorsal fins in the water not far from his boat. The orcas' black heads and backs poked out of the water as they sped towards the carnage.

They were moving with a single-mindedness that made his stomach lurch.

Alicia Delaware was floating nearby. She was holding the head of a young man whose orange suit hadn't inflated. Anawak steered the boat towards her, then he and Stringer hauled the unconscious man and the girl on board. Others were swimming towards them now, stretching out their arms to be pulled out of the water. The boat was filling rapidly. It was much smaller than the Blue Shark and already overloaded. Frantically they kept pulling people in, while Anawak scanned the sea for bodies.

'There's one!' shouted Stringer.

A man was floating motionless in the water, face down, no suit – a protester from the motorboat.

Anawak and Stringer grabbed him by the arms and lifted him.

He wasn't especially heavy.

Not nearly heavy enough.

His head lolled back and his eyes stared blankly. His body ended at the waist, torn flesh, arteries and intestines dangled from the torso, blood dripping over the weaves.

Stringer gasped and let go, then Anawak lost his grip and the corpse splashed back into the water.

All around the boat, sword-like fins swirled through the waves. There were at least ten of them, maybe more. A blow sent the boat spinning. Anawak leaped to the wheel, opened the throttle and sped off. Three vast backs rose out of the water before him. He swerved and the whales dived. Two more appeared on the other side, heading straight for the boat. Anawak swerved again. He heard screaming and crying and panic took hold of him, but somehow he steered the Zodiac past the black-and-white bodies blocking their escape.

There was a crunching sound. He swung round in time to see the Lady Wexham shudder and heel in a cloud of spray. In that split second of inattentiveness, the Zodiac's fate was sealed. A giant tail was already hurtling towards the boat.

The Zodiac flew into the air and flipped over.

Anawak soared up, past a cloud of spray, then plummeted down into the ocean. It was bitingly cold. He kicked with all his might, and fought his way up to the surface. Gasping, he was pushed back down. Seized by panic he thrashed about, paddling madly until, spluttering, he surfaced again.

There was no sign of the boat or any of its passengers. The coastline bobbed into view. He was lifted by a wave and at last he saw some of the others. – half a dozen at most. Then gleaming black blades cut through the surf and dived down. A head jerked under and didn't resurface.

An elderly woman saw the man vanish. 'The boat! Where is it?' she shrieked.

Where was the boat? It was too far for them to swim ashore. The woman's screams became more desperate.

Anawak swam over to her. She saw him coming and stretched out her arms. 'Please! You've got to help me.'

I'm going to,' called Anawak. 'Just try to stay calm.'

'I can't keep my head up. I'm sinking.'

'You won't sink.' He took deep long strokes to reach her. ''The suit won't let you.'

The woman didn't seem to hear him: 'You've got to help me. Oh, God, don't let me drown! I don't want to drown.'

'Don't worry, HI-

Suddenly her eyes widened and she vanished under water. Something brushed against Anawak's leg.

Fear coursed through him. He pushed his upper body clear of the water and looked around. The Zodiac was drifting upside-down. All that separated him and the others from it was a few metres – and three black torpedoes.

As the whales powered towards them, something in Anawak protested. Not once had an orca attacked a human in the wild: they treated humans with curiosity, amity or indifference. And whales didn't attack boats – they just didn't. Suddenly he was hit by a rush of water and a flash of red came between him and the whales. Hands reached down to grab him. Then Greywolf steered towards the rest of the swimmers. He pulled Alicia Delaware out of the water and set her down on a bench while Anawak hauled up a wheezing man. He scanned the surface for others. Where was Stringer?