"Tower of the Medusa" is a 1969 science-fiction/fantasy novel by Lin Carter. It was one-half of an Ace Double, with the other half being Kar Kaballa, by George E Smith. "Tower of the Medusa" takes place in the same setting as Lin Carter's earlier Ace Double, "The Star Magicians". It is also short, even for an Ace Double, with its wide-ranging action taking place in only 100 pages.
Our protagonist is named Kirin, a thief/treasure hunter in the mold of Indiana Jones or Locke Baron, who spends his time travelling across the galaxy taking gems from the brows of idols in exotic temples. While on the run for such crimes, he is attacked by a group of assassins, bizarre "death dwarves", and saved by a jocular and rotund wizard. (Incidentally, the protagonist getting accosted and then rescued by a mysterious benefactor is a common beginning for Ace Doubles). His helper, the wizard Temujin, wants Kirin, the galaxy's greatest thief, to raid the titular Tower of Medusa to steal a jewel called the Medusa. While on their way to do, however, the two are captured by Azeera, the cruel but beautiful Witch Queen, along with her helper, the mind wizard Pangoy. All looks lost---unless the beautiful but scantily clad servant girl who comes to their jail cell is actually a disguised amazon warrior spy---but what are the chances of that?
Lin Carter wrote books about both The Cthulu Mythos and The Wizard of Oz, and this book owes as much to those sources of fantasy as it does to high fantasy or science-fiction. Although the book does make a mention that magic is really sufficiently advanced technology, for narrative purposes, this book is a fantasy story, not a science-fiction one, and a fantasy novel that seems at time to be a parody/homage, full of tongue-twisting names and biologically improbable aliens.
The major problem I had with this story was the pacing: the entire capture by the Witch Queen, which was supposed to be an interlude, takes up most of the book, and what is supposed to be the climax of the book is compressed and anti-climactic. That is a common problem with Ace Doubles, and to be honest, wasn't too much of a problem, as the imagination and fun of the different settings and characters made up for a plot that didn't really make a lot of sense to begin with.