The Metal Monster

The Metal Monster is a fantasy novel by American writer Abraham Merritt. 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 epic adventure starts with a foreword where Merritt is assigned the duty to relay Dr. Walter T. Goodwin's incredible tale of his encounter in the Trans-Himalayan mountains to the world, to let everyone know the terrible fate Goodwin's group barely escaped and the possibility of other such monsters out there.
Plot summary.
Dr. Goodwin is on a botanical expedition in the Himalayas. There he meets Dick Drake, the son of one of his old science acquaintances. They are witnesses of a strange aurora-like effect, but seemingly a deliberate one. As they go out to investigate, they meet Goodwin's old friends Martin and Ruth Ventnor, brother and sister scientists. The two are besieged by Persians as Darius III led when Alexander of Macedon conquered them more than two thousand years ago.
The group is saved by a magnificent woman they get to know as Norhala. 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.
They are led to a hidden valley occupied by what they name "The Metal Monster", a strange metal city occupied by the metal animate Things Norhala commands. This city is governed by what they call the Metal Emperor, assisted by the Keeper of the Cones.
Ruth is slowly being converted by Norhala to become like her; her little sister. Martin, her brother, tries shooting the Metal Emperor, who retaliates with a ray blast, putting Martin in a comatose state.
Closed in between the Metal Monster and the Persians, it falls to Goodwin and Drake to find a way to escape their predicament.
Reception.
This book was a favorite of H. P. Lovecraft, though he at first avoided the revised version, at the suggestion of C. M. Eddy, Jr.. According to his March 6, 1934 letter to James F. Morton:
Copyright.
The copyright for this story has expired in the United States and, thus, now resides in the public domain there. The text is available via Project Gutenberg.
Revisions.
Three versions of the story exist.
The second version is named "The Metal Emperor", appearing in 1927 in Hugo Gernsback's "Science and Invention" magazine. It is an abridged version of the first story, with the leading character's name changed to Louis Thorton.