One smuggler wore a trilby, white with a black band. Another looked like Little Richard. The third was the most worrisome. He had heavy shoulders and a lidless, unsmiling gaze. When a fly landed on his eyebrow, he flicked it off with his eyebrow. We were in Mahajanga, a dusty, sweltering port on the northwestern coast of Madagascar. The restaurant, Baobab, had eight tables, lime-green walls, no other customers, and an unlimited supply of flies. They drowned in the limonade that the smugglers ordered for the table. Cell phones buzzed and lit up. Negotiations in Malagasy. The third smuggler, Mr. Tough, glared. Who was this tall American with an entourage who had walked in off the street asking for angonokas?

He was Eric Goode, a fifty-three-year-old Manhattan hotel and restaurant owner. The animal he wanted to buy was one of the world’s rarest tortoises: Astrochelys yniphora, known locally as angonoka and in English as the plowshare tortoise. Its last remaining habitat was ninety miles down the coast, in scattered patches of remote scrubland around Baly Bay. Poaching, possessing, and selling plowshares are all illegal under Madagascan law, and trading in them is banned by international treaty, which only increases their value on the global black market. Determined collectors in Europe and the United States are said to pay up to a hundred thousand dollars for an adult plowshare.

Goode looked like a determined collector—sweaty, single-minded, furtive, with small, piercing blue eyes and several days’ accumulation of salt-and-pepper stubble. He had three people with him: a young biologist from California named Andrea Currylow; a Malagasy translator named Riana Rakotondrainy; and me. As he spoke, he kept asking, with his hands, about the size of the tortoises that the Baobab smugglers could procure. But the smugglers didn’t trust him.

“I saw you on TV,” the man in the trilby said. “A documentary about W.W.F.”

Goode held out his arms. “Do I look like a wrestler?”

The deliberate misunderstanding did not fool them. Everybody knew that the World Wildlife Fund was involved in protecting endangered species in Madagascar. The smugglers expressed disdain for foreign conservationists who tried to tell Malagasies what they could and could not sell. The Americans were the worst, they said. More phone calls. When Goode said that he was prepared to pay two hundred dollars for a small plowshare, the smugglers seemed to relax. Mr. Tough, who wore a tight-fitting navy polo shirt, had apparently decided that Goode was harmless—just another desperate turtle geek. The tortoises were coming, he said. Did Goode plan to take the animals back to America? Yes? Then he should wrap them in diapers, which would absorb the urine. They would pass uneventfully through baggage screening. Did he have any idea what these tortoises were worth in America? If he preferred, they could be delivered to him “at J.F.K.” That would cost much more, of course. Did he ever find himself in Bangkok?

He did. In fact, Goode had recently made a documentary about Bangkok—the smugglers’ primary market—and other hubs of the illegal-wildlife trade, including Hong Kong and Singapore. But he didn’t mention that.

Mr. Tough went off on a red motor scooter. Across the busy boulevard, Goode could see his friend and employee Maurice Rodrigues secretly filming from inside a café. Goode had sent him away when this deal suddenly started to come together, after a casual inquiry. But Rodrigues had not gone back to their hotel, as ordered. What would these guys do if they discovered they were being filmed?

The man in the trilby established that the white woman with us was not Goode’s wife, his daughter, or his girlfriend. In that case, he announced, he would like to buy her. How much? Banter along these lines followed. Goode had brought Currylow, whom he had met at a turtle conference in Florida, to Madagascar in the hope of persuading her to do her Ph.D. field work in Baly Bay on the plowshare. Little Richard mentioned that plowshares were known to relieve congested lungs. If you kept one under your bed, your breathing got better. C’est vrai. They were good for longevity generally. That was one of the reasons they were so popular.

Mr. Tough returned. He parked the scooter next to the Baobab, on a side street, and lifted the seat so that Goode could see into a bin below it. Two baby plowshares sat in a blue plastic bag. Their shells seemed to glow, each scute deep gold, hexagonal, in a dark-brown frame. Their color enhances the plowshares’ price in China, where gold is considered good luck. Goode took each animal gently out of the scooter. They looked healthy. They were, he estimated, between one and two years old. He set them back and told the men he wanted more tortoises, and would meet them again later in the day.

Back at the Hotel Piscine, on the Mahajanga waterfront, a conference was in progress. Its topic: Madagascar’s tortoises and turtles. Goode, one of the sponsors, had slipped out to conduct a survey of the local black market in plowshares. Now he approached a senior government participant, the minister of environment and forests, for official permission to complete the plowshare purchase. The minister, General Herilanto Raveloharison, a bearded former policeman, seemed taken aback. Was this American trying to embarrass him? He gave his permission, but decreed that the police had to be involved. This would be a sting. They would catch the smugglers in the act.

When Goode and I returned to the Baobab, the mood among the smugglers seemed darker. Where was our translator? (She had declined to return.) My own view was certainly darker, knowing that a police raid might be imminent. I kept thinking about a fiasco that had occurred not far from Mahajanga in the nineteen-nineties. Four Germans on a reptile-collecting expedition had been accosted by gendarmes who suddenly opened fire, killing two of the Germans and a fellow-cop, and shooting out the eye of a third German. I did not want to be caught in the middle of a raid by the local gendarmerie.

The smugglers were irritable. No, the tortoises were not there. An old blue Renault pulled up outside. We were told to get in. Three guys, including Little Richard and the man in the trilby, squeezed in with us. As we drove off, I saw a ministry official who had been posted as surveillance looking carefully past our car, a cell phone to her ear. We drove by a church. I tried to commit our route to memory. We turned in to a deserted, dead-end street, stopping outside a house with “Coifur” painted in red on a wall. The house was set back from the street, behind heavy foliage. Mr. Tough parked his scooter by the wall and opened the seat.

There were four plowshares in the bin, but the two new animals were smaller. Goode produced a fat wad of cash. The smugglers seemed soothed by the sight of it. Goode took only the two larger plowshares, wrapping them carefully in a plastic bag. We all shook hands. Enchanté, enchanté. Goode and I hurried off on foot.