This audiobook is pulp: Non-stop action, impossible odds, unspeakable evil. Gotta love it!
John Sark is the hero who was raised by animals (like Tarzan) in the temperate, twilight zone of Mercury, then captured and civilized. He's a mercenary on Mars now, dealing with humanoid Martians and their extremely nasty pre-humanoid race enemies.
The fights are brutal and frantic yet detailed enough to bring you right into the midst of the action; the suspense is real and tingling. A wonderful listen.