A whale shark looms out of the blue, dwarfing divers Martha Holmes and Mike de Gruy. It's a moment of high drama, a breathtaking encounter with the biggest fish in the ocean. But the intrepid pair came to these Pacific islands to track down another heavyweight - the humpback whale. Surrounded by the mysterious sound of singing whales, their hopes rise. Their persistence pays off when a 35-ton mother with a newborn baby lingers quite unconcerned in front of the camera. For the divers it's the highlight of an eventful trip, and a fitting finale to the Sea Trek voyages.