The qualities that made A Wrinkle in Time popular are all [in The Arm of the Starfish], though the plot and characters are kept under better control. At first the story seems a cloak-and-dagger affair: it teeters on the edge of melodrama, becomes mystical in tone, and, if you read the note in the front matter, appears also to be science fiction. There is a "message," which is more skilfully presented than that of the former book. The characters are alive and possible—including the Jesus-like Joshua, who proclaims his non-belief in a personal God, yet cares about humanity even to the fall of a sparrow. (p. 45)

Alice Dalgliesh, in Saturday Review (© 1965 by Saturday Review, Inc.; reprinted with permission), April 24, 1965.