This book was in a haul I got from a used book sale. If you've ever been to one when it opens you know decisions need to be made quickly lest you be trampled underfoot. So I bought this despite I'm not a big Fritz Leiber fan. The fact that it was a 1972 edition in excellent shape added to the appeal. So I got a nice copy of an out of print book cheap, right? The only problem is it was barely worth reading.This book is 3 stories. The first and longest one shares the title and is the old chestnut about are we the only real humans walking the face of this planet. The idea is fine but the execution isn't. Of the 3 characters, one is a blockhead who takes a hell of a long time to figure out what's going on, one is rather annoying because for the most part all she does is run away from said blockhead and the last could be a manniquin in a store window for all he contributes to the story.Next up is Four Ghosts in Hamlet which is not science fiction. More of a ghost story, it's a one-trick deal that reveals early on who will be behind the mysterious doings. Not very suspenseful.The best story is the last one, The Creature from Cleveland Depths, despite the ye olde heads up the machines are going to take over the joint schtick.Not very original and marginally interesting with occasional corny dialogue sprinkled in sums it up. Recommended only for those heavily into the author.