Lupin and Jigen planed to steal enormous money from a racetrack in New York. Their plan is perfect and the only thing remains is to wait for 6 days. To celebrate the success beforehand, they go to a town. 

Lupin parts from Jigen because he recalls another engagement. Then, Lupin saves a girl, Michelle, being chased by suspicious men. She asks Lupin to steal a diamond from her father in order to stop him from doing evil things. Lupin thinks he can get both money and a diamond 6 days later, and he accepts her request to guard her for 6 days. 

Meanwhile, Jigen meets his old fellow soldier, Ryatte, and they’re talking about another business. Then, Jigen is supposed to spends 6 days with Ryatte before the plan with Lupin. On the other hand, Fujiko and Goemon are planning to steal a diamond at a diamond exhibits. The host of the exhibition is… 

(Source: AniDB)