From the back of the book:
"October 3067 unleashed the horrors of a war not seen since the First Succession War. Yet for the mercenaries of the Inner Sphere, this is a war unlike any in history. With the heart and soul of the mercenary trade annihilated on Outreach, and the very reliability of every mercenary command shaking the foundation of every House - causing some to now consider their most stalwart work-for-hire commands as enemies - mercenaries, from the elite to the dregs, are fighting for their lives... and more importantly, their very reputations.
Classic BattleTech Mercenaries Supplemental Update details the fall-out of the opening years of the Jihad and how it relates to mercenaries. Providing updates on all major mercenary commands currently embroiled in the Jihad, as well as covering the various Hiring Halls, this product also details brand new mercenaries commands springing up from the shattered remains of commands destroyed in these opening Jihad years. Rules for running mercenary commands during this era are also included, along with a section detailing newly premiered battlefield units."