The image of Gatsby

Gatsby was described to be a mysterious person who lives in a huge mansion through out the book so far. When Nick was invited to his party I thought all the myteries of him  would be revealed. At the party Lucille even talked about Gastby killing a person as a  German spy. I think Lucille thought in this way because of the time period. 20's is the period after World War I, thus Lucille might have thought Gatsby got rich because he spied for Germany. When Nick complained about the absence of the host Gatsby, Gatsby informed that he is the host. (I think Nick couldn't have recognized Gatsby at the end of chapter 1, in the dark. He could have just imagined that the person trembling was Gatsby. Otherwise, why couldn't Nick recognized Gatsby at the party?)