The planet ""We Made It"" has a social structure controlled by the elite descendants of ""the Crew"" who control the spare parts hospital. And since criminals are a good source, petty crimesmean capital punishment. The ""Sons of Earth,"" young revolutionaries rebelling against this system, don't have much chance until they are accidentally joined by Matthew Keller who discovers that under pressure he becomes invisible. The most noticeable spare part in this conglomerate is a hyperactive thyroid. . . Mr. Niven's.