It was first serialized in Argosy All-Story Weekly in 1920 and features the return of Dr. Goodwin who first appeared in The Moon Pool.

The two are besieged by Persians as Darius III led when Alexander of Macedon conquered them more than two thousand years ago.

She commands the power of lightning and controls strange metal animate Things, living, metallic, geometric forms; an entire city of sentient cubes, globes and tetrahedrons, capable of joining together and forming colossal shapes, and wielding death rays and other armaments of destruction.

Closed in between the Metal Monster and the Persians, it falls to Goodwin and Drake to find a way to escape their predicament.

According to his March 6, 1934 letter to James F. Morton: Other recent items on my calendar are ... A. Merritt's old yarn The Metal Monster, which I had never read before because Eddy told me it was dull.