From the back of the book:
The Contagion has come; it’s ravaged the world and left you in its wake. The few who are left band together, along lines you never once thought you would agree to. When your enemy becomes the only friend you have left, you make do the best you can.
This book includes essays discussing how to combine multiple monster and supernatural types from the Chronicles of Darkness within a Contagion Chronicle game, including:
An FAQ that covers common rules from all the Chronicles game lines and how they interact.
A full explanation of how magic from Mage: The Awakening interacts with all other monster types.
Essays on banding together as groups, and joining monster-specific groups such as covenants, Orders, and courts.
An essay on sharing Merits, and new Merits to facilitate mixed character-type groups.