In the early 21st century, a probe sent by a coalition of alien races arrives to the Solar System in an attempt to head off the unimaginably vast Xaros armada that moves from one star system to another, wiping out all traces of sentient life. The probe's AI scans the internet and decides to try to help humanity after finding a research paper written by a college student named Marc Ibarra. The probe lands and contacts Ibarra, explaining the coming threat and telling the young man that they only have 60 years to do what they can to save humanity from extinction. The reason the probe chose Ibarra is because he figured out a cheap way to manufacture graphene, which is key to the probe's plan.
Six decades later, the world is in the middle of another cold war between the Atlantic Union and China. The Ibarra Corporation is almost a nation in itself. The corporation is putting together a large mission to colonize Saturn's moons and requests the the Atlantic Union's space navy provide escort to their transport ships in the event the Chinese decide to make good on their threat to stop what they claim is an illegal venture. All transport ships, as well as the escort fleet, have been modified with slip-coil engines, the latest development by the Ibarra Corporation that appears to be a modified Alcubierre drive. According to the corporation, the slip-coil will shorten the trip to Saturn considerably. However, when the probe detects the arrival of the Xaros armada to the edge of the Solar System, it convinces the aging CEO Marc Ibarra to enact their secret plan and activate the slip-coils early. Just as the Chinese attempt to attack the civilian ships, the slip-coils engage, and the fleet finds that things aren't what they used to be. Earth looks devastated, and not a single radio signal can be detected. Each ship receives a pre-recorded message from Marc Ibarra, explaining that the slip-coils were never meant to send the fleet to Saturn. They were meant to hide the fleet from the Xaros in a pocket universe for 30 years. Essentially, they were Ibarra's attempt at building an Ark. His hope was that the Xaros would move on after wiping out humanity, leaving behind only a token force to erase all traces of human existence. Even then, the token force may prove to be too much for the fleet to handle. Another key piece to Ibarra's plan is his granddaughter Stacey Ibarra, who enlisted in the space navy under the alias Stacey Faban.
The series provides examples of the following tropes:
- Alcubierre Drive: This is what the slip-coils ostensibly are. Supposedly, they were to cut the months-long journey to Saturn down to just a few days. In reality, they hid the ships in a pocket universe to wait out the arrival and departure of the Xaros armada, which took about 30 years. Only a moment passed for those in the bubble.
- The Battlestar: The Breitenfeld is an escort carrier with the ability to launch fighters, bombers, marine assault shuttles, etc. It's also armed with several powerful railguns that can even destroy a Xaros orbital with a few shots and can punch clean through any human-made armor.
- China Takes Over the World: By the late 21st century, China has been on the path of aggressive expansion, taking over much of Asia despite the resistance by the western powers. It has not only become powerful militarily, but it also seems to have the best cryptography in the world, allowing them to easily hack Atlantic Union computers, forcing AU to often forego using their more advanced tech in favor of the analog options.
- Death Ray: The primary weapon used by the Xaros is the heat beam that is very powerful.
- Disintegrator Ray: A more powerful version of the Xaros beam that can punch through any armor. If the beam hits a living being, that being is turned to dust.
- Fantastic Caste System: The Toth are stratified into Overlords, Warriors, and Menials. The Overlords don't think much of the lives of their Warriors and Menials, and the same can be said for how the Warriors view Menials.
- I Did What I Had to Do: The Marc Ibarra imprint on the probe's AI explains to Stacey that he deliberately pitted the Atlantic Union against China in order to both spur on progress and to provide useful reasons for some elements of his plan that wouldn't arouse Xaros suspicion. China was given advanced computing technology in order to allow them to easily get around Atlantic Union firewalls and hack their equipment. This, in turn, got AU soldiers to get used to not relying on computerized equipment, since the Xaros are even better at hacking than the Chinese. The threat of China also allowed for Ibarra to request an AU fleet to escort his colony ships in exchange for installing slip-coils on the warships.
- Magnetic Weapons: Standard Space Marine weapons are Gauss rifles, which can be set to either high or low velocity (high for armor and low for people). Soldiers have to swap out not only empty clips but also spent batteries. The armor corps uses heavier versions that can punch through even the heaviest armor and are even dangerous to warships. Gauss cannons are also the primary weapons on fighter craft, while warships are equipped with heavy railguns that can obliterate any hull they hit.
- No Peripheral Vision: In the second novel, a reptilian alien who's training the human marines to fight Xaros drones deliberately alters the parameters of the exercise by adding a second drone above them. They all end up being "killed" in a matter of seconds. The alien explains that humans evolved to think in two dimensions, so looking up in search of an enemy is not a natural behavior. Meanwhile, the Xaros are perfectly comfortable in three dimensions, so being fully aware of one's surroundings is a must for any marine.
- One-Hit Kill: This is the effect of a Xaros orbital firing its main beam at any human ship, no matter how big and strong.
- Our Vampires Are Different: The Toth have figured out how to keep their neural structures going for centuries, but this requires them to constantly absorb the minds of others. And the process is incredibly intoxicating and addictive. The Toth Overlords quickly reduced their own race with that. Even though they've been using cloning to produce Warriors and Menials, the process is imperfect, and they don't get as much of a high or benefit from consuming their minds. After being contacted by the Alliance, they agreed to help them fight the Xaros, but were secretly planning on betraying them and feasting on one of the Alliance species. The race they ended up feasting on were the long-lived Karigole, as their vast life experience made their minds all the more attractive to the Toth. They indulged themselves so much, they drove the Karigole to near-extinction. The only Karigole to survive are four of the soldiers (all male) who were off-world at the time.
- Portal Network: In every system they conquer, the Xaros build structures on a planet or a smaller stellar object that will allow travel between any two such structures almost instantaneously via a wormhole. At the end of the first book, the humans manage to capture the wormhole facility on Ceres, which the Xaros have moved to Earth's orbit for some reason. The probe's AI becomes the facility's control center and uses it to allow humans to interact with the other races that are fighting the Xaros, who use other means of traveling faster than light.
- Posthumous Character: Marc Ibarra dies during the Xaros invasion, but he imprints his consciousness onto the probe, and that personality is used by the probe to interact with the humans who have managed to "sidestep" the invasion. While it initially seems to be nothing more than an interface, it later becomes clear that the Ibarra personality is separate from the probe's AI and can even converse with it as if they were two separate entities. In a way, the digitized Ibarra is a ghost of the original one. He even appears to humans as a ghostly hologram.
- Powered Armor: The Marines wear one of those as standard, consisting of a suit of synthetic muscle, over which armor plates are mounted.
- Armor Soldiers take it a step further, by wearing 15 foot tall "Armor" that they control via neural implants as an extension of their own body, while suspended in a "Womb" of "Amniotic Fluid" that provides life support and nutrition for the soldier inside. This also allows individuals like Kallen, who is quadraplectic and thus wheelchair-bound, to serve in an active frontline combat role. Crosses over into Mini-Mecha as the Armor is less "worn" and more "piloted".
- Pretentious German Motto: The Breitenfeld's motto is "Gott mit uns" (God is with us), which has been used throughout German history.
- La Résistance: An alliance of sorts has been created by the few races that have managed to survive the Xaros onslaught (usually by hiding or fleeing). This alliance sends out probes to look for planets with intelligent life that hasn't yet been wiped out by the Xaros. Oftentimes, they are too late, but other times they manage to arrive just in time, as was the case with the probe that arrived to Earth 60 years before the Xaros invasion. The surviving humans joins the alliance. Stacey Ibarra becomes the human ambassador to the alliance, frequently traveling to its headquarters called the Bastion. The alliance has managed to capture a number of Xaros wormhole facilities, allowing them to interact with one another across light years.
- One Nation Under Copyright: The Toth are ruled by corporations. A Toth Overlord's standing in society is directly dependent on their wealth.
- Recursive Creators: The Xaros appear to be extremely powerful self-replicating machines with an incredible capacity for learning and an unexplained desire to wipe out all sentient life in the galaxy. The Xaros armada consists of hundreds of billions of individual drones that are powerful on their own but can also quickly combined into larger and even more powerful units. In every system they conquer, they leave behind from one to a dozen or so drones as sentries to keep an eye out for any new sentient life appearing in the system, either from evolution or from new arrivals. Should a drone receive a signal from a nearby system, it will begin to replicate exponentially and send a wave of a hundred thousand drones to the signal source. Should that wave fail, a new, even larger wave will be sent.
- The Swarm: The Xaros armada has been moving at near-light speeds from star to star for uncountable millennia, wiping out all traces of sentient life (although, strangely, preserving those races that were already extinct by the time they arrived). Only two races have been able to survive their initial encounters. One did not survive the second encounter, and the other only managed to survive by hiding. And those two races were thousands of years more advanced than humans.
- Unobtainium: Quadrium is an extremely rare and expensive to manufacture isotope of hydrogen. It's a key component in slip-coils, which limited how many ships the Ibarra Corporation could retrofit with the drives. Some of it was also used to manufacture special ammunition that makes it easier to destroy Xaros drones.
- The World Is Not Ready: Zig-zagged. While the probe that arrives at the beginning of the first novel possesses a number of technological improvements that would have helped humans prepare for the Xaros invasion, they're not nearly enough to withstand the armada (as evidenced by the fact that no race in the galaxy has managed to fight back the Xaros and survive long-term, so hiding seems to be the primary way of surviving). In addition, the Xaros would be aware of what technology would be normal for a civilization of that level and would be suspicious of anything that didn't appear to be native in origin. So the probe has to be careful about what tech to introduce and when. The probe's entire plan hinges on the Xaros thinking they've succeeded in wiping out the human race and moving on, leaving behind only a small force to clean up. After the defeat of that small force, though, the probe opens up its data banks and introduces many technological improvements to the human survivors.
