The plane leveled off at an altitude of about 2,500 feet above ground, and Juan Carlos booted up the lidar machine, picking up where they had left off the day before. As the lidar bombarded the canopy with laser pulses, Chuck steered the Cessna in parallel lines across the valley, each four to six miles long, in a pattern that, on the computer screen, looked like a gigantic weaving. The plane was buffeted by thermals, knocked up and down, back and forth, and sometimes sliding sideways in a gut-wrenching fashion. Juan Carlos had been right; it was a brutal and scary ride. But Gross worked the controls with constant finesse and a sure hand.

“We were rocking and rolling pretty good,” Gross said later. “It’s like flying a big spiderweb. It takes incredible skill. You have to fly the middle of the line, and you can’t go sixty feet on either side of that line. You have to slide that plane around, doing all rudders. To stay on the line, in that wind, that was challenging. And you have to hold the altitude and airspeed. I had to climb with the terrain and maintain the same altitude. If the terrain starts coming up, I have to come up with it.”

Through it all, I peered out the window, transfixed. I can scarcely find words to describe the opulence of the rainforest that unrolled below us. The tree crowns were packed together like puffballs, displaying every possible hue, tint, and shade of green. Chartreuse, emerald, lime, aquamarine, teal, bottle, glaucous, asparagus, olive, celadon, jade, malachite—mere words are inadequate to express the chromatic infinities. Here and there the canopy was disrupted by a treetop smothered in enormous purple blossoms. Along the central valley floor, the heavy jungle gave way to lush meadows. Two meandering streams glittered in the sunlight, where they joined before flowing out the notch.

We were flying above a primeval Eden, looking for a lost city using advanced technology to shoot billions of laser beams into a jungle that no human beings had entered for perhaps five hundred years: a twenty-first-century assault on an ancient mystery.

“It’s coming up,” Juan Carlos said. “Right there: two white things.”

In an open area, I could see the two features that he had photographed the previous day, standing about thirty feet apart next to a large, rectangular area of darker-colored vegetation. The plane made several passes as I photographed. Again, they looked to me like two square, white pillars rising above the brush.

We got through the flight without mishap, other than the moment a few hours into the flight when I turned off the lidar machine with my knee as I tried to shift my aching legs. The machine and the pilot’s navigational system were linked, so shutting off the lidar turned off Gross’s navigation. He immediately went into a tight, stomach-sickening holding pattern while Juan Carlos booted the machine back up and I apologized profusely. “No worries,” he said, far less perturbed than I thought he would be.

We finished mapping T1 with enough fuel left over to fly a few lines over T2, twenty miles distant. The route took us over the Patuca River, Heinicke’s “most dangerous place on the planet,” a brown snake of water winding through the jungle. T2 was magnificent and dramatic, a deep, hidden valley shut in by sheer, thousand-foot limestone cliffs, draped with vines and riddled with caves. But recent deforestation—only weeks old—had reached the mouth of the T2 valley. As we flew over, I could see the freshly cut trees lying on the ground to dry out so they could be burned, leaving a hideous brown scar.

At the end of the day, we flew to La Ceiba, on the mainland, to refuel. Chuck had pushed the envelope and we landed with less than twenty gallons of aviation fuel remaining, about forty minutes of flight. But the airport had no fuel and nobody could locate the tanker bringing the resupply. Airport officials feared the tanker had been hijacked by drug smugglers. Juan Carlos called Elkins in Roatán. Elkins put Bruce Heinicke on the problem. After calling around, Bruce learned the truck was still en route, delayed by a blowout.

We couldn’t leave the Cessna unguarded, especially if the fuel didn’t arrive and the plane had to stay overnight in La Ceiba. Juan Carlos and Chuck debated sleeping in the plane, but that wasn’t ideal, since they were unarmed. They finally decided that, if fuel didn’t arrive, they would go to the US Air Force base in La Ceiba and ask the soldiers to stand guard for the night. Meanwhile, Michael Sartori was desperate to get the data and finish mapping T1, so it was agreed I’d head back to the island on my own. Fernández gave me the two hard drives with the data, and I went to the airport desk to see if I could get a commercial flight from La Ceiba to Roatán. There was a flight to Roatán that afternoon but it was already full. For $37 I was able to hitch a ride in the copilot’s seat. The plane looked even less reliable than the Cessna, and as I boarded, Juan Carlos joked about what a pity it would be to lose all that precious data in a plane crash after their hard work collecting it.

I landed in Roatán at sunset and gave the hard drives to Sartori, who snatched them up and disappeared into his bungalow, emerging only once to chow down a couple of lobster tails at dinner. He now had all the data he needed to map T1. Late that night Juan Carlos and Chuck Gross finally landed back in Roatán, exhausted but relieved. The fuel truck had arrived at the last minute.

Sartori had hours of work ahead of him. He had to merge data from several sources: the lidar machine, the GPS ground stations, the GPS data from the aircraft itself, and the data from the IMU. Together, all this would create the point cloud, forming a three-dimensional picture of the rainforest and the underlying terrain. First, he had to wait for Mango to retrieve the USB stick from the GPS unit in Culmi and bring it to Catacamas to upload to the server in Houston; Sartori then had to download the data from Houston. The lights in Sartori’s bungalow were still burning at midnight when I went to bed. Ramesh Shrestha, back at NCALM in Houston, remained awake, pressing him for updates.