Sewell Peaslee Wright 
Vampires of Space [PDF ebook] 

Based on its title, this tale might sound like an absurd bit of space-opera fluff, but it’s actually a deeply engaging story packed with interesting theories and ideas. The "vampires" in question aren’t literal bloodsuckers, but rather are mysterious beings who subsist on the life force of others. It’s a fascinating and thought-provoking tale that will please connoisseurs of classic science fiction.