In 13th century Anatolia, the Kayı Tribe was living in relative peace near the town of Ahlat until the Mongol army arrived under the command of Genghis Khan. Ertuğrul stands between his people and the invasion, fighting with the kind of courage that creates legends. Alongside defending the Kayı, he is also searching for his brother, who has vanished, and the path that search opens leads him into contact with a mysterious Order that has been operating in the region without drawing attention.