Quadrail Series

A series of five books by Timothy Zahn. They can be described as thrillers and murder mysteries set in the classic setting of a long train journey...only it's In Space! But that would be to dismiss them as X Meets Y, and with typical Zahn inventiveness, they transcend that pigeonhole.

The stories are set in the 2080s. Thirty years before, human space probes discovered a mysterious conduit light-years in length, just outside the orbit of Jupiter: this turns out to be a part of the Quadrail network, the only means of faster-than-light travel known in the galaxy. It's a literal set of rail tracks with a train on them, and no-one except the tactiturn Spiders who run the network know how it works. Several races have used the Quadrail to found colonies and build empires, and humanity has joined them as the youngest. The only catch being this: no weapons are allowed on the Quadrail, and thus the Spiders prevent interstellar war.

The main character is Frank Compton, a former agent for Westali (Western Alliance Intelligence) dismissed from his former job and eventually employed by the Spiders instead, assisted by Emotionless Girl Bayta. The first novel Night Train to Rigel covers Compton's early employment and his discovery of the secrets of the Quadrail and the real reason the Spiders need him, while the others continue the setting and their covert war against the shadowy enemy of the Spiders while dropping a few more revelations.

Books in the series:

Night Train to Rigel
The Third Lynx
Odd Girl Out
The Domino Pattern
Judgment at Proteus

Tropes used in Quadrail Series include:

Achilles' Heel: The Shonkla-raa made sure their servants would obey them. Having been created by Shonkla-raa, the Modhri and the Chahwyn (and by extension, the Spiders) become mind controlled after being exposed to a certain sound frequency.
Actual Pacifist: The Spiders and the Chahwyn are incapable of violence. They are trying to overcome this by the third book. By the ending of the fourth, we finally get confirmation that the new class of Spiders, which had up to now limited themselves to shoving people around, are in fact very capable of actively killing other living beings.
Ambiguously Brown: Compton's ethnic background isn't mentioned in the books, but the covers for some reason always represent him as this--particularly odd as Bayta doesn't have a consistent look from one to the next.
- The covers are just silly; the second book's cover has a very blonde Bayta on the cover, and a few pages into it she's described as "dark haired".
Ancient Conspiracy: The Modhri has been around for over a thousand years, although he didn't become active until the past two hundred.
Applied Phlebotinum: The Thread, which enables Quadrail travel.
Artificial Gravity: Shorshic-style vectored force thrusters, and the magic that keeps people grounded inside Tube stations and Quadrail trains.
BFG: Lynx + Hawk + Viper in The Third Lynx.
Bio Augmentation: The Fillies are known for this.
Casual Interstellar Travel: It's not cheap, but if you can pay, you can travel to anywhere the Quadrail has service. Basically, this means you can visit the entire known galaxy.
The Chessmaster: Korak Fayr is a rare example who is also a front-line Badass soldier.
Complete Monster: Kennrick. He has no qualms killing colleagues and random strangers to field test a new weapon.
Corrupt Corporate Executive: Larry Hardin.
Deep-Cover Agent: Applies to all Eyes, Morse in particular.
Emotionless Girl: Bayta
- She does warm up nicely to Frank, and later to Rebekah.
Enemy Mine: The Modhri and Frank team up in The Domino Pattern.
Explosive Decompression: Averted. Apparently enough atmosphere has seeped out of Tube stations into the connecting tunnels so that you'll survive outside of a Quadrail train without a spacesuit. You'll still need to bring your own supply of oxygen, though. Useful, since the main characters have had to go outside a lot.
Face Heel Turn: Especially scary because even best friends and close family can be turned once infected by the Modhri. Frank gets his new job largely because, until Bayta comes along, he works alone.
- Happens to Rastra, Applegate, and Morse
- It appears that McMicking managed to avoid this. Or so we're told.
- The Saarix-5 is originally for Bayta, in case this happens to her.
Faster-Than-Light Travel: Quadrail travel
Film Noir: The setting and atmosphere is brimming with it.
First-Name Basis: Bayta doesn't have a last name.
Hive Mind: The Modhri
Humans Are Special: Averted. The reason why the Spiders chose a human to work for them was because, as the youngest and latest race to join galactic civilisation, the Modhri had had less time to infiltrate them.
- Fans fond of growing Epileptic Trees speculated that the oppressive Shonkla-raa from the past were not a totally extinct separate race, but one of the current races consisted of their remnants. The Domino Pattern revealed they were right, and you guessed it, it's ...the Filliaelians. Huh.
Improvised Weapon: Given that there are heavy restrictions on bringing weapons on the Quadrail, Westali did a study on what could be turned into viable weapons on board. Bellidos Intelligence did them one better. Also, Frank turns someone's poor vintage Harley-Davidson into a mini-arsenal in Odd Girl Out.
Intelligent Gerbil: A mild example, some alien races are described in terms of Earth animals (though this might just be how the human viewpoint character sees them). For example, Bellidos have chipmunk-like faces, Juriani parrot-like beaks, Shorshians dolphin-like snouts, and the Filliaelians horse-like faces - in an Incredibly Lame Pun, humans nickname them "Fillies".
Jedi Mind Trick: Thought viruses, and how the Modhri controls Eyes without turning them into Arms. Also, Rebekah and the Melding have a particularly potent form of this ability.
La Résistance
Magnificent Bastard: The Modhri
Master of Disguise: McMicking
Meaningful Name Bayta
No-Paper Future: Paper money seems to have vanished in favor of "cash sticks" which you plug into payment machines.
Obstructive Bureaucrat: Deputy UN Director Biret Losutu. In a common theme of Zahn's books (for another example, see Borsk Fey'lya from The Thrawn Trilogy), Losutu is NOT infected by the Mohdri--he really is just that unpleasant and obstructive on his own--and it's actually his apparently more pleasant ally Colonel Applegate who's a Modhran walker.
Paranoia Fuel: In-universe.
Perfect Pacifist People: The Chahwyn and the Spiders have been genetically modified to be unable to commit violence, even in self defense. The Defenders are developed to compensate for this weakness.
Planet of Hats: New Tigris seems to be inhabited solely by people from the Middle East. Justified in that it's a recent colony with a small population.
Portmanteau: Frank Compton formerly worked for Westali, which is short for "Western Alliance Intelligence".
Posthumous Character: The Shonkla-raa, former rulers of the galaxy, were thought to be an entire Posthumous race, but it was revealed that they were a genetic strain of sorts of Filliaelians.
Puny Earthlings: Mostly averted, only a few races are physically bigger and tougher than humans, and as a former intelligence officer Compton knows various tricks exploiting Bizarre Alien Biology to help him fight them.
Sequel Hook: all the books end with the main plotline still left unresolved, but the fourth really ups the ante - almost making it look as if the whole quadrilogy so far is merely an introduction.
Shapeshifting: The Chahwyn
Shoe Phone: Frank has a bleeding edge sensor and analyzer built into his reader as well as a listening device detector embedded in his watch.
Shout-Out: The opening paragraphs of The Domino Pattern reference the quote "Space is big. Really big" and cites it as the words of 'a twentieth-century philosopher'.
Something Only They Would Say: Near the end of the first book, Frank works out that Applegate is a Modhran walker because he used the exact same words to describe the coral that Frank had said to another walker, which could only be explained by the Hive Mind.
Space Opera
Stun Guns: The kwi has this setting.
Telepathy: How the Modhri, the Chahwyn, and the Spiders communicate. Also, thought viruses.
Ten-Minute Retirement: Frank in The Third Lynx
The Watson: Bayta. She also is captured and threatened in every book.
Thriller on the Express: well, duh. The fourth book especially; the first three stories happen on trains and outside, but the fourth happens entirely during a single long trip.
Twist Ending: And beginning, and middle...it is a Timothy Zahn work, after all.