A dying man hands Lupin a mysterious diamond known as "Twilight Gemini". It is one half of a larger diamond that holds the secret to a buried treasure. The search for the other half and the treasure leads Lupin and Jigen to the deserts of Moracco. Fujiko's attempt to seduce the diamond from Lupin is interrupted by Sadachiyo, an effeminate, whip-wielding villain. The search for the treasure becomes more complicated as Lara, a beautiful rebel leader joins Lupin, and Goemon seeks only revenge against Sadachiyo.