It’s hard to summarize the plot, but it’s roughly about a father trying to find his son to bing him home, and both live in something that could be a generation ship or the human body or something even more strange.
Lethem can write. His prose is easy to read and it has a certain flow to it, but sadly the plot is less easy to comprehend. The story doesn’t make any sense, we never find out what actually happens or where the main characters really are, and what the point of it all is. There is a certain reading public who may enjoy reading stuff like this, trying to find the hidden meaning of it, but sadly I find it is a weakness of fiction if the author can’t convey what he wants to say without the reader scratching his head in confusion.