The cover and description of this book would have you think that it is traditional horror tale about a haunted apartment building, something in the vein of Stephen King's The Shining. But, in reality, this is a sci-fi novel. The story is centered around the Pendleton, a once upper-crust apartment from the Gilded Age. The building has a history of its residents periodically going insane, and naturally the reader is about to join the Pendleton's current residents in one of those periods.
Suddenly the Pendleton seems to change around the characters and the changes are not positive: bioluminescent grass outside, bizarre liquid metal/humanoid creatures and some entity known as the "One" who is hellbent on "exterminating" every single one of them. The trapped and disoriented residents can recognize this new Pendleton as their home plainly enough, but it is at the same time, quite different. Perhaps the most important difference is the mysterious figure known as "Witness" who roams this new apartment building.
Now, I like science fiction; I like Dean Koontz. In this case, I did not like Dean Koontz writing science fiction. Koontz is a master at writing the suspense thriller, and he's pulled off some good sci-fi in the past. The Watchers was an excellent book (two or three terrible movies but an excellent book). Readers moderately familiar with dystopian fiction will be able to guess where the plot is going early on, and unfortunately once that happens, reading through to the end often feels like going through the motions. Koontz raises some interesting philosophical questions, as all sci-fi should, but while they are relevant questions, they have been thoroughly explored time and again.