One of the tests of great SF is, can it be read over and over again, and still be enjoyed? In the case of Tower of Glass, the answer is yes! Bob Silverberg's powers of invention are at a peak in this book, set about 300 years in the future. Simeon Krug, a mega-tycoon of that time, has an obsession to prove that humankind is not alone in the universe. When he discovers signals from deep space, he sets about building a mighty tower of glass, containing the technology to reply to the signals. His workers are synthetic humans (androids) who he drives on furiously, like a ruthless slavemaster. What he does not realise is that the androids believe he is God! Tension builds and builds as the androids, with some human allies, plot to force him to grant them equality with flesh-and-blood humanity. The pivotal moment of truth comes at last... You will have to read it to find out what happens next! Glorious entertainment.