He claims that from 1421 to 1423, during the Ming Dynasty of China under Emperor Zhu Di (朱棣) the fleets of Admiral Zheng He (鄭和), commanded by the Chinese captains Zhou Wen (周聞), Zhou Man (周滿), Yang Qing (楊慶), and Hong Bao (洪保), discovered Australia, New Zealand, the Americas, Antarctica, and the Northeast Passage; circumnavigated Greenland, tried to reach the North and South Poles, and circumnavigated the world before Ferdinand Magellan. The book has been published in many languages and countries around the world and was listed as a New York Times best seller for several weeks in 2003. Although the book contains numerous footnotes, references and acknowledgments, critics point out that it lacks supporting references for Chinese voyages beyond East Africa, the location acknowledged by professional historians as the limit of the fleet's travels. Menzies bases his main theory on original interpretations and extrapolations of academic studies of minority population DNA, archaeological finds and ancient maps.
Menzies claims that knowledge of Zheng He's discoveries was subsequently lost because the Mandarin bureaucrats of the Imperial court feared that the costs of further voyages would ruin the Chinese economy. He conjectures that when Zhu Di died in 1424 and the new Hongxi Emperor forbade further expeditions, the Mandarins hid or destroyed the records of previous exploration to discourage further voyages. Tan Ta Sen, president of the International Zheng He Society, has acknowledged the book's popular appeal as well as its scholarly failings:
