On February 24, 2010, Tilikum, the largest killer whale at SeaWorld, suddenly dragged Dawn Brancheau, his trainer, into the pool and killed her. Journalist Tim Zimmermann set out to find out why. His riveting account of Tilikum's life, and the history of killer whale entertainment at marine parks, dives into the world of the ocean's top predator. It chronicles Tilikum's capture and separation from his family, and the physical and psychological stress he experienced in marine park pools over some 30 years. It explores Tilikum's involvement in two previous deaths. And it details the inherent risks of using captive killer whales for human entertainment. Ultimately, Zimmermann explains how the life of Tilikum came to mean the death of Dawn Brancheau.