In The Zero Stone, Murdoc Jern … inherits a ring, set with the inscrutable 'zero stone', from his murdered father and is himself caught up in the rapids of interstellar intrigue, drawn on—sometimes literally—by the stone and its secrets…. Andre Norton constructs a mystery from this dull, pitted, grey stone suggestive of the proverbial mountain out of a molehill, building more and more props into the book as it progresses. Initially, the 'present' is dappled by memories of the 'past' and the events leading up to Murdoc's father's death, but by the end everything is very much in order, firmly steered along the pre-set channels of the story and the close of the book is, itself, a 'break for the ads.' before the theme is taken up again in Uncharted Stars.

In Uncharted Stars, Murdoc and Eet [an alien mutant] continue their trail of the Zero Stone, and this leads them, after a succession of adventures, to a dead planet where Eet acquires her true shape. The anticlimax of the end does not warrant the lead-up through two books, particularly when the story is as dependent on luck as this one, a feature becoming more and more prominent in Andre Norton's books. She attempts to liven up the story with practically insignificant events, almost immediately cancelled out, and in so doing gives a hint of near desperation. (p. 108)

S. William Alderson, in Children's Book Review (© 1974 Five Owls Press Ltd.; all rights reserved), Autumn, 1974.