Detective novels are nothing new, and neither are invaders from beyond stories, but you don't get many crossbreeds of the two outside of the hardcore futuristic sci-fi realm. In this regard, Inhuman Beings is an enjoyable treat.
Carroll's novel is tightly written, short and sweet the way detective novels should be. He doesn't skimp on the characters or back story, just the excessive pages of prose some authors veer off in to explain it.
It may seem unusual to complain about getting more than you asked for, but that is my major problem with the novel. The book description promises a lone detective suddenly involved in a subversive alien invasion, and Carroll delivers the goods right away, keeping a steady pace and developing the dangers at a quick and steady pace. However, the third part of the book changes gears with the involvement of government officials that eventually buy into the main character's claims of an alien attack, and a story of a lone man against insurmountable odds becomes a low-budget retelling of Independence Day or Invaders from Mars. It isn't exactly a bad change, but it was the former story I read the book for, not the latter.
Also, as good as the book is on keeping the reader interested in the main character, this is mainly due to the pace and tension his lone crusader status affords him. As soon as he becomes part of an underground force battling the aliens, the tone and feeling of the book is lost, along with a great deal of the tension.
In short, I enjoyed the book that I first picked up to read, but it wasn't the same book I eventually put down.