Sibert Medalist, National Book Award Honoree, and New York Times bestselling author Sy Montgomery dives below the surface to study giant manta rays in Ecuador in this final installment in the award-winning Scientists in the Field series. On the vast Pacific, the ocean heaves and sighs like a beating heart. But dive beneath the surface, and angels appear. Giant manta rays-wider than a car is long, with wingspans stretching up to twenty feet-glide past with balletic grace, then vanish into the murky blue. They can soar to depths of nearly a mile, race at twenty-two miles an hour, and live more than fifty years. With the largest brain of any fish on Earth, they are among the ocean's most intelligent and mysterious creatures. But even the most magnificent creatures are fragile. Because mantas grow up slowly-reaching maturity only at seven to ten years-and raise just a single pup once every few years, they are uniquely vulnerable. Only recently did scientists discover that these "angels of the sea" are hovering on the edge of extinction. Bestselling author Sy Montgomery joins scientist Michel Guererro and his team to search for mantas in Ecuador's plankton-rich waters, record their sightings, chart their locations, and note their behaviors and the conditions around them. The work will test and challenge them. But as they struggle and learn, they will also be transformed by their encounters with one of the largest, most mysterious, and most imperiled beings ever to swim the sea.