The first original Trek story published–and, indeed, the only such book published during the initial airing of Star Trek–is Mack Reynolds's Mission to Horatius, published in 1968.

The Enterprise has been out on patrol for a long time, and just when they were heading for a much needed break, they are ordered to a distant star system–Horatius–from which a distress call has originated.

Horatius has three colonized planets: Neolithia, Mythra, and Bavarya. Neolithia was colonized by people who wanted a less technologically dependent way of life, and its inhabitants have only very primitive technology–not even iron. Mythra was colonized by people fleeing religious persecution, and is ruled by a small class of religious elites. Bavarya, the most recently settled, was colonized by political dissidents, and its leader is a militaristic man called Nummer Ein. The Enterprise is not welcomed by the inhabitants of any of the three planets, but they have a duty to determine who called for help, and render aid if they can.

Meanwhile, the Enterprise has troubles of its own. It has been far too long since the crew has been planetside, and Dr. McCoy fears an outbreak of space cafard, a deadly psychological condition caused by the extreme ennui of protracted space travel. If the crew of the Enterprise don't get leave soon, they may tear themselves apart from the strain.

Mission to Horatius is a quick, easy read. With its A plot of the Enterprise investigating a distress call, its B plot of McCoy's concerns about space cafard, and a good dose of comedy, it reads very like an episode of the show. Which is not to say that it's the most well-written possible book, of course. Kirk is rather cavalier in his response to the situation in which he finds himself, and his actions are not what one would expect of an ambassador of the Federation (as Kirk calls himself). He repeatedly ignores the wishes of the governments of the planets they're visiting, despite himself noting that he must not do that. He even says, "We shall see what our Bavaryan bullyboys have to offer," when it is Kirk himself who is acting the bully.

While not flawless, Mission to Horatius should be an enjoyable read for young audiences, for which it was intended.

Notes

In the introduction, John Ordover (editor at Pocket Books who was in charge of the Trek books at the time) recounts how he first encountered the book as an eight-year-old in 1970, and dedicates the reissue to "every Star Trek fan who was ever eight years old." (Reynolds, 1968/1999, p. 8)

In Voyages of Imagination, he elaborates: "We reprinted that for fun! Paramount has the rights; the original publisher is out of business. It's not going to cost us much to do a facsimile of this. It was selling for $50 at conventions. So why not do a reissue?" (Ayers, 2006, p. 131)

The original painted cover artwork by Richard "Sparky" Moore sold at auction for $5,500 on 2019-04-23. (Heritage Auctions, 2019)