The tower of the title is a miles-high crystalline tower being built in the tundra of the high Arctic. It is a device for extraterrestrial communication. Its sole purpose is to answer a cryptic radio message received from deep space years before.

The message is enigmatic, mysterious. It is simply a sequence of random numbers, repeated over and over again. It seems to have no meaning, but it is clearly of artificial origin. It is definitely a message from an extraterrestrial intelligence, not some natural phenomenon. But that is all that can be said for sure about it.

The tower is part of an enormous tachyon transmitter, designed and built at great expense to simply answer the radio message, instantly. Its message is simply to announce our receipt of the radio
signal, that we are listening and we are ready to talk.

The tower, its associated structures, and the enormous facilities built for its construction are incredibly expensive, and the philanthropic pursuit of a single fabulously rich tycoon. Governments have refused to build it since there is no guarantee its new technology will work. This is the work of a one man, a ruthless financial and scientific genius.

But the tower is being built with blood money. The business which is financing the project has developed artificial human beings, like the replicants in Blade Runner, except they are identical to human beings. No test or science can distinguish them from humans, except that they are all surgically sterilized so they cannot reproduce, and their skins and internal tissues are dyed a bright red so they cannot possibly pass themselves off as human. The builder of the tower has successfully lobbied for legislation to ensure that these androids are biological machines, property, and have no human or civil rights. They are slaves, pure and simple, and they are valuable because they can be forced to work. They are capable of doing not only manual labor and dangerous or unpleasant tasks, but they can be educated to be skilled laborers and even scientists, managers and professionals. But by law, they are not human. And they work for their owners.

The society in which all this takes place is ambivalent about all this. There is a political movement to declare these replicants as real human beings, and both humans and some of the replicants are involved in the political process to overturn the statutes that keep the redskins chattel. The movement is broad and multifaceted. There are conventional peaceful political organizations "working within the system", and there are out-and-out terrorists, and everything in between.

The hero of our story is the son of the tycoon, who bitterly disagrees with his father's view of the replicants as slaves. And he has a lot invested in the problem. His mistress is a replicant. A highly illegal act for him, and a death sentence for her if the news gets out. As the story progresses, he slowly puts together the fact that his lover is a member of a resistance group, and they are planning a sabotage action to bring the tower down by melting the permafrost foundation that keeps it stable and upright.

I found some interesting parallels between this novel and William Golding's (of Lord of the Flies fame) novel "The Spire", about the building of a huge cathedral tower in medieval England.