20 April

Lyons, France

Bernard Roche felt a pang of guilt for not having dealt sooner with the water samples. But how was he to know that a lobster could kill a man – and that it might kill more?

Jean Jérôme, the chef-poissonnier at Troisgros in Roanne, had failed to emerge from his coma and had died twenty-four hours after the contaminated Brittany lobster had exploded in his face. It was still impossible to say what had caused his death, but one thing was clear his body had never recovered from a severe toxic shock. There was no real proof that the lobster or, indeed, the substance found inside it – was to blame, but it certainly looked that way. Other members of the kitchen staff had been taken ill, but the worst affected was the apprentice who had put the mysterious substance in the jar. They were all suffering from dizziness, nausea and migraines, and had difficulty concentrating. It was no laughing matter, especially for Troisgros, which was in danger of closing its doors. But what really worried Roche was the number of people who had consulted their doctors with similar symptoms since Jérôme had died. Their cases weren't nearly as critical, but Roche feared the worst, especially now he knew what had happened to the water in which the lobsters had been stored.

For the sake of the restaurant, the press had tried to play down the story, but the incident was reported, and Roche was hearing rumours from elsewhere in the country. Troisgros was not the only establishment to have been affected. In Paris several people had died, allegedly from shellfish poisoning – but Roche suspected there was more to it than that. He'd heard similar news from Le Havre, Cherbourg, Caen, Rennes and Brest. One of his assistants had agreed to look into it and a story emerged in which the Brittany lobster played an unsavoury role. In the end Roche put aside his other work and devoted himself to analysing the water samples.

In no time he found yet more unusual chemicals, whose presence he couldn't explain. He needed fresh samples urgently, so he made enquiries in all the relevant cities. Regrettably no one had thought to preserve the substance. The lobster in Roanne was the only one to have exploded, but elsewhere people talked about unpalatable lobsters that they'd been forced to throw away or lobsters that had been leaking before they were cooked. If only everyone had had the presence of mind demonstrated by the apprentice at Troisgros, but Roche knew that fishermen, wholesalers and kitchen staff couldn't be expected to respond like scientists. For the time being he had to rely on speculation. In his opinion the lobster had been inhabited by two separate organisms. First there was the jelly, which had disintegrated, leaving nothing behind.

Then there was the other organism, which was very much alive and in plentiful supply. Something about it seemed ominously familiar.

He stared into his microscope.

Thousands of transparent spheres were rolling around like fast-moving tennis balls. If he was right in his assumption, inside each sphere was a coiled pedunculus – a kind of feeding tube.

Were these the organisms that had killed Jean Jérôme?

Roche reached for a sterilised needle and jabbed it into the tip of his thumb, producing a tiny droplet of blood. With great care he injected it on to the sample on the slide and looked through the lens. Magnified to seven hundred times their normal size, Roche's blood cells looked like ruby-red petals, each one packed with haemoglobin. They mingled with the water. The transparent spheres sprang into action, unfurling their tubes and falling on the human protoplasm. The peduncles entered the cells like miniature cannulae and the sinister micro-organisms took on a reddish hue as they sucked the blood cells dry. The assault on Roche's blood intensified: as soon as one cell was empty, the micro-organisms turned to the next, swelling all the time, as Roche had expected. Each could hold the content of ten cells. In less than forty-five minutes their work would be done. He watched, fascinated: the process was much faster than he'd believed.

Fifteen minutes later the frenzy was over.

Roche sat motionless next to his microscope. Then he noted, 'Query Pfiesteria piscicida!

'Query' stood for any lingering doubt, but Roche was sure that the agent responsible for the sickness and death had been identified. What truly unnerved him was that it seemed more monstrous than Pfiesteria piscicida, which made it a double superlative, since Pfiesteria was already thought to be a monster – albeit of just one hundredth of a millimetre in diameter. It was one of the smallest predators on Earth – and one of the deadliest.

Pfiesteria piscicida was a vampire.

He'd read a lot about it. Scientists' acquaintance with it was relatively new. It had started in the 1980s with the death of fifty fish in a laboratory at North Carolina State University. At first there was no apparent problem with the water in which they were swimming: the aquarium was swarming with tiny unicellular organisms, but that was nothing new. So the water was changed and new fish brought in. They didn't last a day. Something was exterminating them with incredible efficiency. It killed goldfish, striped bass and Nile tilapia in hours, sometimes minutes. Time and again the researchers watched as the fish twitched, then died an agonising death. Again and again the mysterious micro-organisms appeared out of nowhere, then vanished just as fast.

Slowly they pieced things together. A botanist identified the sinister organism as a new species of dinoflagellate. Numerous types had been categorised, some of which were harmless, but others had been exposed as living sacs of poison. They were known to have contaminated mussel farms, and certain species were responsible for the feared 'red tides' that turned the water red or brown. Shellfish were affected too. But these dinoflagellates were nothing compared to the newly discovered organisms.

Pfiesteria piscicida was different from other members of its order. It actively attacked. In some ways it resembled a tick – not for its appearance, but for its extraordinary patience. It lurked in the sediment of riverbeds or seas, seemingly lifeless. Each individual was encased in a protective cyst, and survived for years without food. All it took was a shower of secretions from a passing shoal of fish to trigger its appetite.

A lightning attack ensued. The algae cast aside their cysts, rising through the water in billions. Each cell was driven by a pair of flagella, one of which rotated like a propeller while the other steered. As they settled on a fish, the cells released their toxins, paralysing the creature's nervous system and burning coinsized holes in its skin. The peduncles shot into the wounds and sucked the lifeblood from the victim. Then they sank back to the seabed and retreated into their casing.

By and large, toxic algae were seen as normal, like poisonous toadstools in a wood. People had known of the phenomenon since Biblical times. Exodus contained a description that seemed to fit perfectly with the red tides: 'And all the water in the Nile turned into blood. And the fish in the Nile died, and the Nile stank, so that the Egyptians could not drink water from the Nile…' For a fish to be killed by a single-cell organism was clearly nothing new. But the method and the degree of brutality were. It seemed as though the planet's water had been seized by a terrible sickness and, for the moment, the most spectacular symptoms bore the name Pfiesteria piscicida. Toxins were killing marine life, coral was succumbing to new forms of disease, and beds of algae had become infected. But all of this was merely a reflection of the true state of the seas, which were suffering the consequences of overfishing, chemical dumping, the urbanisation of coastal regions, and global warming. No one could agree on whether the invasion of killer algae was a new development or a periodic occurrence, but there was no doubt that it was spreading across the globe to an unprecedented extent and that Nature had once again demonstrated her infinite creativity in producing new species. In Europe people congratulated themselves that Pfiesteria had not yet reached their shores, but thousands of fish were dying off the coast of Norway, and the Norwegian salmon farmers were facing financial ruin. This time the killer organism was Chrysochromulina polylepis, a kind of baby brother to Pfiesteria. No one dared speculate what might come next.