Battletech Legends Lethal Heritage by Michael A. Stackpole

A DANGEROUS NEW ENEMY APPROACHES…

Two decades after the events that nearly brought the Successor States to the brink of all-out war, the Great Houses exist in an uneasy peace.

But from out beyond the Periphery comes a new threat. A swift-moving military force of unknown origin. Nothing the Inner Sphere has can stop them. Their power, speed, and ferocity are unparalleled. Some of the finest warriors and ablest units have challenged them and been crushed. No force has faced them and won.

They are the Clans! A military juggernaut whose sole reason for existence is battle. A race that selectively breeds itself for combat.