The moon is inhospitable to human beings in many ways. Even its light gravity is threatening: "With gravity one-sixth as strong as it is on Earth, you must spend at least two hours out of the twenty-four keeping fit, or your very bones will atrophy." For pioneers like Mark, Tom, and Judy, each day may bring new discoveries of unexpected dangers. Their parents "died when a pit collapsed, two years ago"; unpredictably, iron alloy beams become brittle on the moon and break, and in the case of Mark's parents, the discovery that iron alloy was unsuitable for shoring up mines proved fatal.

The pioneers, in order to survive, must pay careful attention to their environment, never allowing panic to make them break the rules that help safeguard their lives. When Mark takes his turtle, a slow vehicle, out to rescue Kamolondo, he follows a prescribed path that has...