There are two House of Crimson & Clover Prequels. It is not mandatory to read these before the main House of Crimson & Clover series. Whether to read them before Volume I, or later in your series journey, is largely a matter of preference.
The Storm and the Darkness is the first prequel, with Shattered being the follow-up to that story.
Click on the covers below to visit the site for each book.