In the year 570 CE, a child by the name of Muhammad is born in the Arabian city of Mecca. Sixty-two years later, he dies, and upon his death, the faith that he founded, Islam ("obedience to the one God"), dominates the western half of the Arabian Peninsula. By the end of the first millennium CE, four centuries after the death of Muhammad, Islam has grown to dominate western Asia, north and east Africa, the Levant, and the Iberian Peninsula.

The Holy Lands are lost to Christianity, and Christian Europe is under siege. Folk tales begin to circulate - their origins obscure, but first noted in historic texts around the 12th century CE - of a lost Christian kingdom in the East, the Kingdom of Prester John. There resides the patriarch of Saint Thomas, who proselytized in the Orient. Later, in the 15th century, under the impetus of the Portuguese King Henry the Navigator, Portuguese missionaries and navigators enter the Indian Ocean from the south and, creeping northward up the east coast of Africa, hear ever more substantial tales of a Christian kingdom lost in the belly of Islam. As they enter upon the coast of Somalia, competing in a growing trade in slaves and gold with Arabs of the peninsula, they become increasingly interested in the source of this legend, in part to fulfil the centuries-long dream of discovering the Kingdom of Prester John, but also in part to secure the alliance of a Christian power against the force of Islam.