Across the undefined boundary of the crocodile-swollen river, the formerly French, Finland-sized Republic of the Congo is somehow the "good" Congo. Once part of French Equatorial Africa, it gained independence in 1960 and has been relatively civil-war-free since 1999, with a corruption index, according to Transparency International, on par with that of Bangladesh. While there are laws against poaching, adherence to them is something else: it's not hard to find reports of chimpanzee meat in Brazzaville markets, mandrill parts and leopard skins at the port, or ivory smugglers filtering through nearly every porous border. Some here describe smoked gorilla palms and thumbs as a delicacy, although others say one outcome of Ebola is it's made ape meat slightly less appealing.

Nearly two-thirds of the country is forest, which is where 125,000 of the world's estimated 150,000 to 200,000 remaining western lowland gorillas live. To meet Bermejo and reach Mbomo, I've taken a two-hour flight to the Mboko landing strip inside 5,250-square-mile Odzala-Kokoua National Park, declared in 1935 and wedged inside the country's northwest border. It's October and rainy season--promising for spotting gorillas, since the precipitation produces fruit, which draws the apes from the thick undergrowth into the trees--but right now the rain's pounding the little Cessna's fuselage in thick cloud cover, even while the autopilot's warning system kicks in--"Terrain. Terrain. Pull up. Pull up." Then the white evaporates. The forest stretches on forever.

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After Bermejo lost 221 of her 238 apes to Ebola, she didn't head home, instead focusing her attention on people. While some scientists worked on an Ebola vaccine (intended for humans and gorillas alike, but never achieved), Bermejo came to believe that creating community projects was the best way to prevent hunting and poaching, while simultaneously demonstrating the value of the pristine forested land. When she'd first arrived in Africa in 1986 as a 22-year-old to study chimpanzees in Senegal, the director of the national park would combat poachers by dropping grenades on them by helicopter.

She'd come to Congo with her husband, German Illera, a Spanish law student-turned-videographer and naturalist, whom she'd met at the University of Barcelona. He was every bit as passionate about Africa as she. "Then we both got sick. It was in the middle of Ebola, back in 2003, and we each got symptoms within the same two hours. That's the only time I asked myself what I was doing in Africa," she says. "You can imagine our relief when we found out it was only malaria."

Committed to the Congolese villagers and the apes they loved, she prospected the area for new groups of gorillas and discovered thick densities of them in 2009 in a 12-square-mile area, just seven miles from Odzala-Kokoua's border, and one mile from the nearest road. "I was amazed at how protected these gorillas were when very little kept them from the village," she remembers. "But the elders had decided to defend them. One day a gorilla was sitting in the middle of that road, and a village woman was scared. So I sent a tracker to help her cross, and when she got to the other side, she turned and waved to the ape. That's when I knew this was the right place to establish the new camp." It took Illera a year of bushwhacking to connect the gorillas' trails through the lush marantaceae, or arrowroot, forest to the new ones he cut, which allowed the area to be mapped. Today there are 50 miles of paths dividing this area into 75 quadrants, allowing six resident groups of 120 gorillas to be studied. It takes eight men a full month twice a year to maintain the trails, or the forest will swallow them up.