Since the dawn of recorded history, humans have felt a kinship with the sleek and beautiful dolphin, an animal whose playfulness, sociability, and intelligence seems like an aquatic mirror of mankind. In recent decades, scientists have discovered dolphins recognize themselves in reflections, count, feel despondent, adorn themselves, rescue one another (and humans), deduce, infer, form cliques, throw tantrums, gossip, scheme. Several native peoples trace their lineage to dolphins. They are the stars of multimillion dollar aquatic theme parks, money that has fueled a sinister illicit trade as shown in the documentary Blackfish. The U.S. Navy has a secret program using dolphins as undersea soldiers. The theory that they are a superior, extraterrestial species is popular among the New Age fringe. They are the victims of brutal slaughters as depicted in the documentary The Cove. To swim with a dolphin is a transporting experience, an encounter with a being seemingly so like us, yet so alien. No writer is better positioned to portray these magical creatures than Susan Casey, whose combination of personal reporting, intense scientific research, and evocative prose made The Wave and The Devil's Teeth contemporary classics of writing on the oceans. For two years Casey traveled the world, and now she has written a thrilling book about the other intelligent life on the planet.