THE SQUID HUNTER.(searching for giant squid thought to inhabit the seas near New Zealand, with marine biologist Steve O'Shea)

An interview with David Grann.

On a moonless January night in 2003, Olivier de Kersauson, the French yachtsman, was racing across the Atlantic Ocean, trying to break the record for the fastest sailing voyage around the world, when his boat mysteriously came to a halt. There was no land for hundreds of miles, yet the mast rattled and the hull shuddered, as if the vessel had run aground. Kersauson turned the wheel one way, then the other; still, the gunwales shook inexplicably in the darkness. Kersauson ordered his crew, all of whom were now running up and down the deck, to investigate. Some of the crew took out spotlights and shone them on the water, as the massive trimaran--a three-hulled, hundred-and-ten-foot boat that was the largest racing machine of its kind, and was named Geronimo, for the Apache warrior--pitched in the waves.

Meanwhile, the first mate, Didier Ragot, descended from the deck into the cabin, opened a trapdoor in the floor, and peered through a porthole into the ocean, using a flashlight. He glimpsed something by the rudder. "It was bigger than a human leg," Ragot recently told me. "It was a tentacle." He looked again. "It was starting to move," he recalled.

He beckoned Kersauson, who came down and crouched over the opening. "I think it's some sort of animal," Ragot said.

Kersauson took the flashlight, and inspected for himself. "I had never seen anything like it," he told me. "There were two giant tentacles right beneath us, lashing at the rudder."

The creature seemed to be wrapping itself around the boat, which rocked violently. The floorboards creaked, and the rudder started to bend. Then, just as the stern seemed ready to snap, everything went still. "As it unhooked itself from the boat, I could see its tentacles," Ragot recalled. "The whole animal must have been nearly thirty feet long."

The creature had glistening skin and long arms with suckers, which left impressions on the hull. "It was enormous," Kersauson recalled. "I've been sailing for forty years and I've always had an answer for everything--for hurricanes and icebergs. But I didn't have an answer for this. It was terrifying."