This reprint is of a lower-than-fax quality.
Take page 19 for instance: the seven coins of the original edition are reproduced as seven black spots.
This is a good book, but you better buy a used copy of the original edition instead of this grimy reprint.
Cumont's work is generally considered to be the quintessential work on the Mithraic cult. His book presents a well researched and easily readably description of this religion. Mostly he focuses upon how the religion was spread in the Roman Empire, where it originated and some of its basic dogmas. However, if you are looking for a description of the secret initiation rituals you will have to look elsewhere. While he does mention these rituals in brief, there is no extensive description or analysis on them.