The Master Key is an odd story-- some people claim that it's early science fiction, but it's not, really, it's exactly what the title might imply: fantasy with the trappings of science. It's about a boy named Rob who accidentally summons the Demon of Electricity, a genie who grants him three electrical devices a week for three weeks. These include a flying machine, a stun gun, food pills, a device that let's him see anything in the world at any time, and the Character Marker, a device that (quite impressively) reads the electrical fields of the body to see if a person is Good, Evil, Wise, Foolish, Kind, or Clever. Rob has a lot of zany adventures with these, of course, which range from fun (his foiling of coups in England and France) to tedious (his capture by the Turks) to fantastically racist (his encounter with a group of African cannibals). But the end of the book is deflating-- Baum's point was that humanity was not ready for the fantastic progress that the Demon brings, and Rob decides to return all the devices to the Demon. It's a good point... but not necessarily enjoyable reading. Rob becomes increasingly disillusioned with his devices as the story goes on, and so does the reader. But this perhaps makes it a piece of sf after all: in the venerable tradition of Frankenstein, it's a rumination on scientific progress and the costs and dangers it brings.