Thrown into the mix are espers, men and women capable of using terrible mental powers like telepathy, teleportation, pyrokinesis and telekinesis. Considered to be less than human, espers are used as tools by the Empire, judged to be too dangerous to be allowed their freedom.

Mistworld introduces Investigator Topaz, who appears in Deathstalker War, the third book in the Deathstalker trilogy. Investigators are a group of men and women whose job is to study newly discovered alien species and determine how much of a threat they might be to the Empire. Depending on their findings, the aliens are then enslaved or exterminated. Everyone in their right mind fears Investigators, as they are unsurpassed killers, trained from childhood to be cold, efficient, unmerciful killing machines. Not only is Topaz an Investigator, she is also a Siren, the only Investigator with esper powers in the Empire. When she turned rogue and left the service of the Empire, they sent an army of five hundred men to retrieve her. She killed them all with a single song, a devastating mix of esp and voice. She fled to Mistworld, the single place of refuge for Outlawed individuals. Mistworld is the Empire's dumping ground, a cold inhospitable rock populated by traitors, criminals, and runaway espers. The Empress Lionstone XIV would love to destroy Mistworld but it is too heavily guarded by Mistworld's espers. Mistworld tells the story of the Empire's latest bid to destroy this place of refuge and Topaz's efforts to stop it.

In Ghostworld, we are given a glimpse of the past of Captain John Silence and Investigator Frost, two of the Empress' loyal servants who play an important role in the Deathstalker trilogy. We see how they first form the bond that they share in the later novels. Silence, Frost and their team are sent to the Rim World of Unseeli, to investigate the lack of communication from Base Thirteen, a mining settlement. Captain Silence is chosen because he has previous experience on Unseeli; he was responsible for destroying the entire native population when they failed to submit to the Empire. On Unseeli he and the others are forced to deal with the ghosts of the decimated natives, Silence's old friend-turned-traitor Carrion, and an alien ship which has crashed near Base Thirteen.

The third novel, Hellworld, introduces Captain Scott Hunter, a captain given the choice between being cashiered out of the Imperial Fleet or volunteering for a near suicide mission, joining the Hell Squads. The Hell Squads are "volunteers" sent to investigate new worlds prior to colonization. Hell Squad missions are one-way; if the scouts survive, they are allowed to live out the rest of their lives on the new world. Hunter and his squad are sent to Wolf IV, an inhospitable, storm-tossed world. After a near-disastrous landing, they begin exploring, only to find that they are not the first to visit the planet. They discover an ancient city on Wolf IV, and before they realize it, they awaken a race of sleeping aliens. In order to survive they must destroy the aliens, but not before they determine what the aliens are and where they came from.

Simon R. Green has a particular style which most readers will immediately like or dislike. His books are filled with larger-than-life, in-your-face heroes and heroines. The stories center around men and women who have superhuman abilities, who are stronger, faster, better fighters, better thinkers, or have esper talent. The villains are big and bad and so are the "heroes" who deal with them. In the Deathstalker universe, the Imperial government and the aristocracy are corrupt, there is the constant threat of alien invasion(s) hanging over everyone's head, and there is intrigue, espionage, and a rebellion looming. In short, a rich background to base countless stories in, three of which are told in Twilight of the Empire.