Among Thieves is a prison novel masquerading as something more. The action centers on an intramural riot, in which good and evil alike are presumably unmasked. However, by that time the reader is past caring since he has been overwhelmed by Mr. Cuomo's prolixity, much of which has neither significance nor pertinence. The pivotal character, a petty criminal named Mel Simmons, is the victim of ""society"" and just as inadvertently killed during the riot. Samuel F. Fleishman, Ph.D., Assistant Warden, who is intended to be a more sympathetic type, comes across instead as Mr. Belvedere retained by Bellevue as a comparison shopper. The third character, an innocent named Johnny Mancino, is perhaps the least unreal of all but as it turns out, he is only ballast. The overall impression is that while it is extremely difficult to write a dull novel about prison life or a prison riot, Mr. Cuomo has succeeded very well. This in spite of two hopeful, earlier novels and in spite of the big sell behind this one a commercial candidate. And a Literary Guild selection.