The series focuses on a number of parallel worlds, and the world of Centrum in particular. A number of individual learn how to open portals into Centrum from their native worlds. Note: people can only open portals between their own worlds and Centrum, while the natives of Centrum are unable to open any portals. Each person's method for opening a portal differs, as does the size and duration of the portal. In the case of the first book's protagonist, his portal opens behind him and lasts only a few seconds.
The world of Centrum used to be about a century ahead of Earth in technological development. Right around their equivalent of the early 20th century, the world was struck by a calamity known as the "plastic plague". The plague (speculations range from some kind of radiation to bacteria and even nanobots) dissolves all polymers on the planet in a matter of hours, including oil deposits. This resulted in a social collapse and the shattering of a single empire into numerous territories. The technological development has also stalled and even rolled back, with coal once again becoming the primary fuel source. That happened two hundred years ago, and Centrum still hasn't recovered, in large part because the plague is persistent. Any polymer brought to Centrum from another world survives for two-three hours at most, before melting into goo.
The disparate territories are joined by the railroaders (who run all steam trains and maintain communications between the territories) and the border guards. The Border Guard Corps is primarily made up of off-worlders, the vast majority of which are from Earth, which is one of the most advanced known worlds. Their task is to patrol the likely exit points for interdimensional visitors. Many of these are first-time travelers, who have just discovered their personal way to open a portal to Centrum, completely by accident. A large percentage isn't capable of recreating the conditions. They are given a choice: stay on Centrum for good, or be taken back by a guide. Those who do manage to figure out their method are usually left with two different choices: join the border guards or become a smuggler.
The series is currently made up of 10 novels:
- Outpost (2013), Sergey Lukyanenko
- Reverse (2014), Sergey Lukyanenko and Aleksandr Gromov
- AWOL (2014), Sergey Lukyanenko and Mikhail Tyrin
- Renegades (2015), Sergey Volkov
- Recruit (2015), Vladimir Vasilyev
- Collector (2016), Dmitriy Kazakov
- Synthesis (2016), Sergey Slyusarenko
- Wings (2016), Valentin Holmogorov
- Rift (2017), Valentin Holmogorov
- Origin (2018), Sergey Lukyanenko and Valentin Holmogorov
No relation to the Borderlands video game franchise.
The series contains examples of the following tropes:
- Amicable Exes: Striker and Agel used to date, but Agel's preference for BDSM didn't sit right with Striker, so he ended up breaking it off. They remained friends after that, and she also dated several men in his outpost. It turned out to all be a way for her to smuggle the plague bomb to Earth. While she may have indeed cared for Striker, she would never let that interfere with her mission.
- Apocalypse How: Centrum was hit by something they call the "plastic plague", which destroy all polymers, effectively stopping progress in its tracks. They suffered a near-total social collapse, although some territories recovered more quickly than other. Source agents are trying to do the same to Earth, and the results would be even more devastating, given our increased reliance on polymers over the last century. Thousands of planes would fall out of the sky, patients would die in hospitals, all electronics would fail, PVC pipes would dissolve, oil would disappear, nuclear reactors would meltdown. It's estimated that 2-3 billions would die during the first several months. Mass starvation would set in, resulting in cannibalism and more deaths. Ironically, the less developed third world nations would survive more or less intact.
- Base on Wheels: Railroaders prefer to keep their HQ mobile. The triumvirate that rules them never stays in one place, or together for that matter. Each has his or her own armored train that prowls the vast tracks all over Centrum.
- Break Out the Museum Piece: During the climactic assault in Outpost, Geezer brings out the World War One-era Maxim gun he has stashed in the armory only a few weeks before. Justified, since most modern machine guns are more likely to have polymers in them, making them useless in Centrum. According to Geezer, he purchased it legally, in a non-functional condition, but he's a pretty good machinist and manages to restore it to full working condition.
- Chekhov's Gun: Outpost starts with Striker chasing a smuggler, who jumps away before Striker can detain him, leaving behind a backpack full of a variety of batteries, which are illegal in Centrum. At the end, he discovers that the "batteries" are, in fact, components of a Source device, whose purpose is to bring the "plastic plague" to Earth. And he inadvertently brought them to Earth when he took the backpack with him, planning to turn it over to the proper authorities but never getting the chance.
- Crazy Enough to Work: In Outpost, when Striker, Fiddler, Hop, and Agel reach the Rift, they learn that the Rift can't be crossed on a train, since the only thing spanning it a flimsy bridge suspended on thick ropes. The locals only cross it in handcars to deliver mail and small cargo items to a train waiting on the other side. When the second train takes off without waiting for them, they come up with a crazy plan to take their train across the Rift, pointing out that Fiddler can probably open a large enough portal to get them all out in case the bridge collapses. The bridge does end up collapsing, but they're close enough to the other side of the Rift that the whiplash from the snapped ropes actually sends the train flying to the other side. The train is totalled, but everyone aboard is fine. The craziness continues when Striker comes up with an idea to convert a handcar into a rocket-propelled vehicle using a local artist's acetylene torch as a rocket, welded to the handcar. They end up having to get out and push to give it a headstart, but the handcar picks up speed after that. But then, a few miles from their goal, the rocket goes out... and they keep rolling. Agel explains that they've actually been going slightly downhill all this time, so the rocket may not have actually done anything.
- Deep Cover Agent: In Outpost, it's eventually revealed that Agel is a Source agent. She replaced the original Agel after the latter's death many years ago. All her sleeping around with the guards of Outpost 16 was partly a way to convince one of them to take her to Earth, so she could smuggle a plague bomb there and do to Earth what her people have already done to Centrum.
- Dimensional Traveler: Many people have the potential to learn to open portals to Centrum. But it usually requires very specific circumstances, and a person can go an entire life without learning to open a portal. Or they may do it once and see the portal form and wink out in a split-second and simply wonder what the hell that was. Striker, the protagonist of Outpost, really dislikes his method: he has to be naked, wet, make drying motions with his hands, and step back. The portal opens behind him, which is highly unusual. Another man opens a portal whenever he's afraid. A girl on their outpost can only open one after being insulted. Striker figures out how to open a modified portal at the end of Outpost without doing any of those actions, having realized that the process is entirely mental, so all he has to do is reach that particular state of mind.
- Eco-Terrorist: It's heavily implied that Source agents are this. They seem to genuinely believe that they have saved Centrum and want to save Earth. When Striker points out that billions would die, Agel simply shrugs and claims that it's our own fault for not developing in a more harmonious way.
- Elective Broken Language: Striker's ex-girlfriend Agel (a native of Centrum) can speak Russian, but she does so with a heavy accent (her grammar is fine, though). However, he later learns she's only been faking the accent and can speak Russian perfectly well. She's not actually from Centrum but from the world of Source, seeking to do to Earth what her people did to Centrum two centuries ago.
- Elective Mute: One of the border guards at Outpost 16 never speaks, so everyone just assumes him to be mute. One time, though, Striker is shocked to see him walk out of his portal singing a song. When confronted, the guy is forced to admit to having a stutter that strangely disappears only when he's singing, so he prefers not to speak in general. But he has to sing to open his portal.
- ET Gave Us Wifi: Striker learns in Outpost that the Border Guard Corps took advantage of the chaos of the plague to steal a number of technologies from Centrum and use them to accelerate Earth's development during the 19th and early 20th centuries. Averted with all modern tech, which is entirely our own, since Centrum is stuck in Medieval Stasis. The inverse is also possible, as Agel tells Striker that someone hired a think tank on Earth to come up with blueprints for a nuclear bomb without using polymers. If the designs were to be smuggled to Centrum, it could start a nuclear arms race.
- Instant Expert: A downplayed example. Anyone who travels to Centrum for the first time has their learning ability boosted Up to Eleven for several days. The effect repeats itself with every trip, but diminishing every time, until it's not even noticeable.
- Jumping on a Grenade: During the assault on Outpost 16, one of the mercenaries tosses a grenade into the building. Fiddler reacts first and leaps onto the grenade, saving the others in the process. He lives for a few more seconds, before dying.
- Medieval Stasis: Centrum has been stuck in at the 19th century level of development for over two centuries, and this isn't likely to change given the lack of oil and the impossibility of keeping polymers from dissolving in Centrum. In Outpost, Source agents are trying to do the same thing to Earth, except the consequences would be significantly worse, since polymers are ubiquitous in our society.
- Portal Cut: Generally thought to be impossible, since it's believed that a portal requires open space to appear. Striker dismisses Geezer's claims to have appeared in the ocean once for this reason. Striker witnesses Agel's portal sever the arm of one of her fellow Source agents. During the climax, he opens his own portal right on top of Agel. Most of Agel's body falls into the portal, but she loses An Arm and a Leg. He assumes she dies from the shock and the blood loss shortly after.
- Resurrective Immortality: On one world, humans are The Ageless. But they die every week, like clockwork, only to come back to life several minutes later. It usually takes a few hours for all their memories to come back after death. It's not uncommon for people to date those with the same death day (to the point where personal ads might say "Blonde, fit, pretty, Saturday", with the latter indicating the person's death day), as it's convenient to die and resurrect on the same day, especially since it's usually followed by furious sex. Violent death "doesn't count". People always come back after it, only to die again on their designated death day. Trying to kill yourself on your death day usually results in two deaths - terribly inconvenient. It's pointed out that the resurrected person isn't exactly the same as the one who died. There are subtle personality differences that build up over time.
- Suspiciously Similar Song: After being abandoned in a Centrum city by Geezer, Striker quickly picks up the Clondal language and joins a band playing at a local club. He gives the band fresh material by translating popular Earth songs into their language and adapting it for them. One song he's working on just as Geezer finds him is Sting's "Englishman in New York". He points out that, in the original song, it's weird for a guy to walk down a New York street with a cane, whereas canes are popular in Centrum. So, their new song "Earthman in Centrum" has the singer point out that everyone has a cane but him. He also helped them adapt songs by The Beatles. When another band member complains that he's tired of copying songs, another one brushes it off, claiming that nothing's original anymore.
- You Are in Command Now: After the events of Outpost, Geezer opts to retire and (possibly) work for Border Guard Corps counterintelligence. Striker is unanimously chosen as the new Outpost 16 commander.