Barry Simmonds, a small-time lawyer in Belize-a former British possession on shores of the Caribbean, discovers a trail that leads to Switzerland as he manages the probate of a recently deceased associate. In the Geneva Freeport, the world's largest and most secret art and valuables storage facility, he finds an ancient and valuable codex of what appears to be a descriptive herbarium.

Simmonds, in financial difficulties following the collapse of a real estate project he was developing in San Pedro with a group of questionable Russian investors, decides to find a buyer for the codex.

He meets Sir Patrick Kennedy, a banker and rich collector, in San Sebastian, Spain, and comes to an arrangement with the aid of Anna Basurko, an archaeologist.

Kennedy has Anna translate the codex and uncovers an astonishing secret, one that had been guarded by the high priests of Montezuma-the last king of the Aztecs, and transmitted to Franciscan friars following the Spanish conquest of Mexico.

However, what Simmonds had not counted on was his Russian investors' determination to get their money back and by whatever means necessary, including violence and murder.

The Gilgamesh Quintet, is a collection of the five episodes of The Gilgamesh Project serialised in 2020 and 2021.