This true story of high adventure and equally high indignation is as stirring as any fictional thriller. The adventurer is David McTaggart, a Canadian-born and California-ruined developer, who in 1972 was looking for a way to rebound from his business and marital failures. The way he chose -- or, rather, as he tells it, the way that chose him -- was to sail his 38-foot sloop Vega from New Zealand to Mururoa atoll, about a thousand miles southeast of Tahiti. It was not a pleasure cruise. McTaggart and his two-man crew were sailing into the heart of the French nuclear test zone. Their purpose was to disrupt the tests by heaving to downwind of the fallout.

To this day McTaggart cannot quite explain why at the age of 40 he suddenly turned radical. He was not one of those people who are born seething. He was looking for purpose in his life at the same time that the Canadian Greenpeace Foundation was looking for someone to take on the French. He abhorred the practice of setting off nuclear explosions in the atmosphere, but there was more. "Something inside of me said that if I didn't go," he writes, "I would be making a mistake."

Under international law the high seas -- where the bombs would explode and where McTaggart took care to station Vega -- is everyman's land; no state may validly exercise sovereignty there. Indeed, France had not even bothered to justify its maritime zoning under domestic law. As the sloop approached the test area, McTaggart and company were legally unassailable.

The French Navy was ill-prepared for North-American-style protest. After delivering a couple of ignored warnings, the commanding officer decided to terrorize McTaggart. First one ship made as if to collide with Vega, only to sheer off at the last moment. Then two ships came at her, one on either side -- a 640-ton tugboat and a 400-ton minesweeper. Dumbfounded, McTaggart held course. One of the pair came within 15 yards of smashing into Vega's stern and missed the other ship by the same margin.

When the ships turned around and began to steam back for another go at Vega, her crew resorted to a desperate act: they lowered her sails. As McTaggart explains, "Our only hope now was to leave the French with a situation where they would have to bear down on a stationary vessel. There was too much machismo in the air... The only way to break up the madness was to go limp."

The gambit worked, at least for a while. The French ships retreated. A few days later, while Vega was out of position, the French detonated a bomb. A few days after that, when the sloop was back in place, the minesweeper charged again. This time, however, there was no last-second veer. The minesweeper rammed Vega broadside.

Apparently this was a botch. The French had wanted to scare the bilge out of Vega but not to strike her. To make amends they towed her to the atoll and patched her up, and the admiral had McTaggart and crew to lunch. But Vega was still crippled, and McTaggart was broke. He flew home to Canada hoping to enlist the government's support in a damage suit against France.

Canada made sympathetic noises but took no action. (McTaggart's explanation is that, while publicly deploring atmospheric testing, Canada was secretly selling uranium to France.) Most of McTaggart's friends drifted away from him: The conservatives among them considered him a lunatic, and the radicals thought him co-opted for having lunched with the French admiral. Spending the winter on the rainy British Columbia coast with his New Zealand lover, Anne-Marie Horne, he "began to feel an almost breathtaking loneliness."

He fought his way out of his depression. The next summer he, Anne-Marie, and another couple set sail again for the atoll, where France had scheduled another round of tests. This time the navy did not equivocate. When Vega entered the zone, the commanding officer dispatched a goon squad, who boarded the sloop and beat the protesters with truncheons. Their blows drove one of McTaggart's eyes back into his head. Anne-Marie managed to photograph the beatings, hide the camera below deck, and plant an identical camera in plain view. The French seized the dummy camera, but Anne-Marie still had to go through a gauntlet of searches but managed to smuggle the roll of film past her captors. Some of her photos appear in the book, capturing te French hitmen's faces in their methodical viciousness.

The last phase of McTaggart's campaign took place in the French courts. Represented by an inexperienced but dogged attorney, he eventually won a half-baked settlement. More important, stung by the publicity which the case generated, France renounced further atmospheric testing.

But, unlike the heroes of made-up thrillers, McTaggart did not come through his exploits unscathed. He had to sell Vega, he almost lost his eye, he lived for months in Paris on three dollars a day. And Anne-Marie was unable to stick it out with him. Yet, for all the anguish they caused him, McTaggart's actions were among the most effective in the history of protest. Though it has no means of self-expression, the planet itself owes him its thanks.