Galactic Derelict continues the series' premise, an encounter between Western heroes and a mysterious alien race that has used time travel to alter Earth.

Kirkus Reviews comments for this novel "Andre Norton has no peer in his [sic] chosen field of science fiction for teenagers ... [here] there's a hint of racial antagonism."

While seeking water for his cattle, Travis Fox enters a little known canyon in the Arizona desert and gets captured by three men, one of whom he recognizes as Dr. Gordon Ashe, an archaeologist.

Disguised as Folsom hunters, Fox, Ashe, and Ross Murdock travel into the past to scout out the area around the wreckage of an alien starship, a sphere perhaps 120 feet in diameter.

After receiving the scouts' report via transtemporal telegraph, Major Kelgarries and several technicians come into the past and examine the small ship, determining that they can shift it directly into the present.

On the day the transfer is to be made, ash from a volcanic explosion and a stampede of mammoths drive the three men into the ship along with Case Renfry, an electronics technician.