From the back of the book:
Kell Hounds, Northwind Highlanders, Blue Star Irregulars. Literally a thousand and one mercenary units populate the Inner Sphere, yet these are the house hold names that captivate teh common man. But for every top, there is a bottom. Gray's Ghosts, Kraken Unleashed, Vinson's Vigilantes. Some call them 'pirates,' others 'down-on-their-luck,' and others 'salvation' when the job's small enough and the pay just right. But for these hard-boiled warriors, life isn't cheap. Life hardly exists at all!
A companion volume to Classic BattleTech Field Manual: Mercenaries, Revised and Mercenaries Supplemental, Mercenaries Supplemental II delves into the dregs of the mercenary world, allowing players to use these unique mercenaries in their Classic BattleTech campaigns. Additional rules for mercenary creation include non-BattleMech Unit Tech Levels, special renegade and freelancer mercenary paths, as well as rules for playing mercenaries in different BattleTech eras, from the Star League, to the Succession Wars, to the present.
The original paperback edition was produced in 2005 by FanPro, and still crops up in online stockists although it's officially out of print, and an electronic version is available from the current licence holder, Catalyst Game Labs.