Fleeing his birthplace in Brittany to escape the Baron de Tournemine, who killed his mother, and seek his lost father, Mathurin Kerbouchard looks for passage on a ship.

Hearing that his father is dead, Mathurin goes inland and poses as a scholar in Córdoba, but his scholarship is interrupted when he becomes involved in political intrigue surrounding Aziza and is imprisoned by Prince Ahmed.

Leaving Spain, Safia and Mathurin take up with a merchant caravan and travel across Europe, stopping along the way at places to trade or to fight off thieves.

Mathurin kills the baron and, leaving the caravan, later throws de Tournamine's body into a swamp rumored to be a gate to Purgatory.

Stalling for time as the caravan drives south toward the Black Sea, Kerbouchard exchanges pleasantries with the Khan, fights a duel with Prince Yury, and receives a drink.

Kerbouchard returns to the caravan, which is approaching the Black Sea, and assists as they contrive rudimentary fortifications, hoping to hold their ground against the Petchenegs until boats arrive to take them to Constantinople.

A battle ensues, by the end of which most of the caravan merchants are killed, but Suzanne may have escaped in a small boat, and Mathurin, wounded, hides in the brush and nurses himself back to health, surviving to reclaim his horse, and ride to Byzantium, clothed in rags.

Casting out storyteller Abdullah and taking his place in the market in Constantinople, Mathurin makes some money and an enemy named Bardas.

Leaving Constantinople, Mathurin travels by boat across the Black Sea to Trebizond and adopts the identity of ibn-Ibrahim, a Muslim physician, scholar and alchemist.

Invited to visit the Emir Ma'sud Kahn, Mathurin presents a picture of himself in his identity as ibn-Ibrahim, and, learning that ibn-Haram is in the city, decides to pass on from Tabriz toward Jundi Shapur, the medical school that provides his pretense for travelling through the area.

Leaving Tabriz, Mathurin and Khatib travel alongside a caravan as far as Qazvin, where ibn-Ibrahim receives gifts and an invitation to visit Alamut.

Brought before Sinan, Mathurin reveals some of the details of his past that Mahmoud had kept secret and broaches the subject of alchemy, hoping to be kept around longer.

Afterward, Mahmoud approaches with guards and escorts him (along with his bags, which contains his surgery equipment) to a surgical room, saying that he was brought to Alamut on an errand of mercy to save a slave's life, by making him a eunuch.

In the garden, Mathurin packs his powder into pipes there, plugs the ends, and fashions wicks from fat-soaked string, and they hide until the middle of the next day.

Along his long journey the main character is thrust into the heart of the treacheries, passions, violence and dazzling wonders of a magnificent time.

From castle to slave galley, from sword-wracked battlefields to a princess's secret chamber, and ultimately, to the impregnable fortress of the Valley of the Assassins in the heart of Persia.

[2] Despite L'Amour's stated desire, neither continuation of this novel was ever published, presumably due to his declining health, which eventually led to his death four years later, in 1988.