The story centres on Kayla Reinumon, a gladiator on a backwater planet who is asked (not very politely) to participate in the titular Empress Game. The fight determines who marries the heir to the Sakien Empire's throne, and although it's supposed to be a princesses-only event, one particular aspirant to the throne lacks combat skills and wants Kayla to secretly take her place. Kayla is motivated by a secret about her past that she wants to keep: she's already a princess anyway, having survived the massacre of her family when the empire conquered her homeworld. Accepting the deal provides a convenient escape from those looking for her, but at the same time, plunging into the heart of imperial politics isn't exactly free of problems. She has to keep her secret from her new "allies" (some of whom, as it happens, were involved in the aforementioned massacre), while also dealing with the traitor who sold her homeworld to the empire in the first place, who has his own interest in her. And then there's the little matter of winning the Empress Game itself.
The series contains examples of:
- Apologetic Attacker: There's a degree of this from Janeen after she betrays Malkor's team, as she keeps saying that it "wasn't supposed to be like this" and that nobody was supposed to get hurt. However, it's a pretty poor apology, since it's peppered with self-justification and blame-shifting along the lines of "if you'd only accepted it peacefully, it wouldn't have come to this".
- Becoming the Mask: Kayla fears that this will happen after Isonde is put in a coma by an attack, since Kayla's temporary imposture then becomes indefinite.
- Blood Sport: Gladiatorial combat is fairly common, and Kayla is the reigning champion of one particular arena. It's on a backwater planet, but she's good enough to attract attention from people who want her to (secretly and illegally) fight in the titular Empress Game, which has similar rules but is supposed to be determining who marries the Prince.
- Body Double: Kayla is recruited to be this for Princess Isonde. However, it's not just in case of attack it's for a whole gladiatorial tournament, which Isonde needs to win despite having no fighting ability. When Isonde is put into a coma by a surprise attack, Kayla has to take over Isonde's political games as well.
- Body Paint: Kayla wears body paint while fighting in the arena. It's mostly black, with dark red slashes this imitates the colouring of the animal she uses as her Nom de Guerre.
- Dirty Mind-Reading: Done second-hand. Contrary to what Malkor thinks, Kayla can't read his mind, but Corinth can, and his comments indicate that Malkor's thoughts about Kayla are along these lines.Corinth: It's a loop between "Can she read my thoughts? Is she doing it right now?" and "Shit! Don't think that! What if she heard it?" You're so messing with him.
Kayla: I'm not doing anything.
Corinth: He doesn't know that. He thinks you [awkwardly] Oh. Oh, wow. He definitely doesn't want you to hear that. I'm not sharing that one.
Kayla: I don't want.
Corinth: [blushes] Yeah you do.
- Duel to the Death: The gladiatorial combat in which Kayla participates is often brutal, but Kayla herself prefers to incapacitate her enemies rather than kill them. Later, in the Empress Game itself, the duels are not to the death, which Kayla notes is sometimes to her advantage if she actually had to damage her opponents rather than just score points, she'd have a tougher job, since some of them could take more damage than she could.
- Electronic Telepathy: Dolan's speciality using technology to replicate, enhance, and deploy Wyrd telepathy. The things he did with it, though, caused him to be stripped of his own psi powers and exiled. They didn't seem to consider that his technology might allow him to regain his powers.
- Emergency Impersonation: Kayla is supposed to impersonate Isonde in combat during the Empress Games, but Isonde gets sent into a coma by means of a toxin; as such, Kayla has to take over full-time, including the political and social games which Isonde would normally handle.
- Enemy Mine: It gets complicated. Blame for the conquest of Ordoch can be attributed both to the IDC (which planned it) and to Dolan (who led the Empire there in the first place). Kayla is willing to work with an IDC team while opposing Dolan, since she thinks there's a possibility of freeing Ordoch that way. Meanwhile, Tia'tan is pursuing the same objective by working with Dolan against the IDC team. She and Kayla each accuse the other of being a traitor on account of the alliances they made. Then they team up themselves.
- Engagement Challenge: Prince Ardin is required to marry whichever princess wins a special gladiatorial tournament. In fact, he's already in love with a perfectly good princess, but she isn't any good at fighting thus, scheme is hatched for Kayla to impersonate Isonde in the arena and win them the marriage that they both want anyway.
- Everything's Better with Princesses: The Sakien Empire has no shortage of them, and the titular Empress Game is a gladiatorial combat between them. The protagonist impersonates one (and secretly, is one from a different place). That said, "princess" is defined fairly broadly daughters of non-monarchical authority figures (religious leaders, for example) seem to qualify as well as royalty.
- Feudal Future: Both major societies featured (the Sakien Empire and the Wyrd planets) have monarchies.
- Hidden Backup Princess: Kayla and her brother Corinth are the only survivors of the massacre of the Ordochian royal family, and are in hiding. Only it turns out they're not the only survivors, because the others were secretly captured alive for Dolan to use in his experiments.
- Holographic Disguise: Kayla and Isonde each have one of each other, allowing them to change places when it's time for Kayla to impersonate Isonde in fights. It takes a little work to get them right.
- Mind Manipulation: Wyrd psi powers can, in some circumstances, control other people's actions. Malkor is naturally nervous around Kayla after finding out that she's Wyrd, though in fact, she doesn't have her psi powers any more.
- Mysterious Past: Although readers learn who Kayla is fairly quickly, she takes great pains to keep her past mysterious to Malkor and the other imperials.
- Nom de Guerre: Kayla fights in the arena under a sort of stage name; she doesn't like revealing her real one, and even after she accepts the deal which starts the main plot, she still refuses to disclose her real name to the people she's now working with.
- Psychic Static: With training, it's possible for imperials to block out Wyrd mind-reading, but apparently not to the extent that Imperials sometimes seem to think. Corinth comments that Malkor's blocks are "pretty effective, for an imperial", but that being nervous largely negates the effort.
- Spectator Casualty: These are keenly expected at the arena in which Kayla fights. It's part of the entertainment, and the crowd cheers.
- The Speechless: Kayla's brother Corinth hasn't spoken aloud since the deaths of the rest of their family, but he does speak to her telepathically. That's okay when they're alone, but since they're trying to keep their background secret (and telepathy would give the game away), it's problematic when in company Kayla can't always use telepathy back, and there's a risk she'd respond aloud to something he'd only said telepathically.
- State Sec: The Imperial Diplomatic Corps seems more a spy agency and security force than a real diplomatic service, though it's possible it has actual diplomatic functions we don't see.
- Synthetic Plague: The Sakien Empire created a nanotech virus as a bio-weapon, but it got loose and is doing a lot of damage. This caused the Empire to invade the planet of Ordoch, which had refused to provide a cure on the grounds that the technology involved could have created an even worse weapon, and the Empire had already demonstrated itself unfit to be trusted with that kind of thing. However, the Empire still hasn't managed to compel Ordoch to produce a cure, and can't hold the planet in the long run.