Nick Nomad and the Hammer of Lemuria by Myles Campbell

Nick Nomad and the Hammer of Lemuria is a pulp adventure novel set in the 1930's. Nick, an ex-marine, blames himself for his fiance's death, wallowing in self-pity, until Gwen Chen, an alluring nightclub singer, skilled martial artist and Chinese resistance fighter, bursts into his office. She is being hunted by the "Scorpion," a fanatical officer in the Japanese army who is determined to find the lost weapons of mass destruction that were built by ancient Lemuria for a war against Atlantis. When Gwen is captured, Nick and his best friend Alan, a quirky museum curator with an encyclopedic knowledge of Lemuria, must rescue Gwen, and the three of them embark on a globe-spanning journey to defeat the Scorpion and save the world.