The Golden Scorpion by Sax Rohmer

The Golden Scorpion linked the story lines developed in the Yellow Claw (1915) with Dr. Fu Manchu who appears but is not named. "He wore a plain yellow robe and had a little black cap on his head. His face, his wonderful evil face I can never forget, and his eyes -- I fear you will think I exaggerate -- but his eyes were green as emeralds!"