CASPers - Combat Assault Systems, Personal - are the lords of the future battlefield. The massive mechs were created to give humanity an edge against the rest of the mercenary forces in the Galactic Union. Just like today's tanks, though, massive amounts of armor and weaponry just make the CASPers "hard to kill", not "invulnerable". There are things in the galaxy even stronger than the CASPer, and when humans run up against them, it's up to the human inside to figure out a way to snatch victory from the jaws of defeat.

It's the 22nd century. Humanity has taken its first steps into the galaxy, and we've found ourselves in a vast playground of alien races and cultures. As the newest players on the universal stage, though, we're at the bottom of the food chain. Welcome back to the Four Horsemen universe, where only a willingness to fight and die for money separates humans from the majority of the other races. While some of the stories deal with mercenaries, others introduce listeners to the other guilds, organizations, and races that make up the landscape of the Four Horsemen universe.

The plot by the Galactic Union’s Mercenary Guild against the Four Horsemen has culminated in an invasion of Earth. Faced with an overwhelming force, the human mercs had no choice. They’ve fled, leaving Sansar Enkh to go to the Mercenary Guild headquarters on Capital Planet to stand trial for humanity. On the run, Jim Cartwright and Nigel Shirazi have travelled to the Winged Hussars’ secret base of New Warsaw, in an effort to convince Alexis Cromwell to join the fight, while the other mercenaries who escaped the fall of Earth have gone to the perceived safe haven of Karma.

War has come to the worlds of Humans. The rich planet of Tau-Rietzke, however, is far from Earth and the Mercenary Guild’s invasion, and its alien-registered mercenary companies are a safe haven for humans on the run. Organizations like the Midnight Sun Free Company. Having just completed another successful mission and taken possession of three Raknars, it was party time for Saisho Branco and the Midnight Sun personnel, and they were enjoying a little down time...until the war spilled over into their corner of the galaxy and two competing organizations showed up to steal the Raknars.

Peacemakers. The Galactic Union's most capable enforcers and resolute negotiators, their name alone elicits fear and awe among the Union's citizenry. Having completed a harrowing confirmation mission, Jessica Francis stands ready to become Earth's first Peacemaker and believes obtaining her commission is a mere formality. However, certain members of the Guild question her ability. Worried that she'll fall back on her mercenary ways, they want Jessica to prove her mettle.