This title describes a walk with a dinosaur, as two teams of scientists race to bring back to life the long-extinct woolly mammoth, using DNA from a frozen mammoth discovered in a cliff face in Northern Siberia. Advances in medical and scientific technology mean that the impossible is now theoretically possible: a mammoth can be cloned from a frozen, long-dead mammoth corpse. But it's not easy. No one knows for sure how long frozen mammoth sperm keeps. Elephant sperm keeps well, but the mammoth has been extinct for at least 4000 years. But the mammoth remains a vividly real image: huge, with great curving tusks it is both utterly familiar and completely unknown. The discovery of a frozen mammoth in a crumbling Siberian cliff face attracted two teams of scientists, one French, one Japanese, to attempt to recreate it. At issue is both a moral and a technical question: is the preservation of species through improved reproductive biology to be applauded? Does this extend to reviving extinct species? And, if so, which should tread on the Earth's surface again, defying their Darwinian extinction? Combining an adventure story with a depiction of contemporary scientific powers, the book is both a drama and cautionary tale of two teams of pioneers as they approach the moment when they can play God: they will decide if the woolly mammoth walks again.