Veteran diver Hwang Byung-joo, former Marine Han Jae-myung, and Busan tough guy Baek In-tak gather their diving gear and head to the sea. There, where the sounds of 'ascent' and 'descent' are the only things breaking the silence, the divers push through collapsed walls and tangled compartments, searching for a thread of hope until the very end. An untold story, 'Logbook', unfolds its first chapter to the world!