The story begins with the premise that a huge glass tower is needed to communicate with an extraterrestrial civilization. 
Simon Krug, the man behind the endeavour, has created humanoids to achieve the task. 

This book brilliantly approaches relevant themes such as purpose, divinity, slavery and what it means to be human as a whole. 

I found, however, that the story could have had half its size without loosing anything meaningful. The story was so slow and so many unimportant characters were introduced that I found myself skimming through some pages.