An Unexpected Direction for the Series
Mostly Harmless
I'm not certain what inspired the writing and development of a fifth Hitchhiker's Guide to the Galaxy novel. Comments from the author at the time stated that he had been in a bad place mentally at the time of writing and that the resulting work wasn't really something he was happy with. I can understand that; book four, So Long, and Thanks for All the Fish, was such a perfect conclusion for the series, a way to send everyone off to their happy places and tie up the story in a satisfying way. Why a fifth book was needed is a real question.
Of course, Adams died before he could continue this story past the fifth book and that left any number of fans left sad not only because of his death, naturally, but because this fifth book ended up acting as a conclusion of the series, and a rather dark one at that. Now, sure, a collection of the authors writings and unfinished works, The Salmon of Doubt, had a half-written Dirk Gently novel that the author stated would likely have been rewritten into a Hitchhiker novel instead, but that didn't happen. Instead, Mostly Harmless remained the last word on Hitchhiker.
The problem with the novel: damn, is it bleak. The story starts with Arthur and Fenchurch, the love of Arthur's life who he found in the previous novel. As they travel across the galaxy, enjoying the universe together, they suddenly hit a pocket of dimensional instability and, before he knows it, Fenchurch disappears, sucked away into a different dimension which Arthur could never reach. Not that he doesn't try, continuing to fly across the galaxy for months, taking every flight he can to find a way to follow Fenchurch. In the process he sells everything he had on him, and then blood and sperm, all to fund his attempts at finding Fenchurch again.
That ends when the star-liner he was on crashes into a planet, killing everyone but him. That planet, Lamuella, is a pretty remote and backwards place with a tribe of human-like beings who worship the mighty Bob (a god made up by the tribe's "wise-man"). Arthur discovers, while on the planet, that he has a knack for making sandwiches and becomes their great and revered sandwich maker. This gives him many moons of happiness as he focuses solely on sandwiches while ignoring everything that went wrong in his life. His idyllic existence is ruined, though, when Trillian shows up, dragging a teenage kid behind her who, apparently, is Arthur's. Trill went and had a kid with Arthur's donated seed but, now, Trillian has to go and cover a massive war on another planet (as she now works as a reporter) and so she dumps the teen girl, Random Dent, on her father. Arthur, naturally, has no clue what to do with this.
Meanwhile, Ford has his own shocking discovery. While at the Guide offices, looking for a way to get in and get out with his paycheck without, you know, having to fill out any paperwork or do any actual work, he discovers that the Guide has been remade. The business was purchased by a shadowy venture and, of all things, they planned some nasty new version of the Guide (with the word "Panic" printed across it's sleek black front). This sends Ford spinning, a version of Guide 2.0 in his pocket, and soon enough he's crashing on Lamuella, ruining the rest of Arthur's existence, causing Random to run off, and sending all of them on a venture that leads back to Earth... right before it gets blown up by the Vogons. Again.
So let's be fair to Mostly Harmless: it does try to push some ideas forward. The big plot line of a shadowy corporation buying up the book, the titular guide from which the series drew its name as well as many of its more comedic asides, works. It adds some needed menace to the novel and creates something for the heroes to fight against. Had this been a bigger focus of the book (without spending so much time on Arthur, watching his life fall apart again and again), that might have been something quite interesting.
Additionally, I don't hate the idea of Arthur spontaneously having a teenage daughter. I don't think the way the books goes about doing this, punishing Arthur despite him having done nothing wrong (which shows that mean-spirited edge that Adams regretted after the fact), but in concept having him spontaneously have a daughter, maybe from another dimension where Arthur and Trillian actually did get together for a while, kind of works. It's a concept, at lest, that the novel could have explored, forcing him to step up and be an actual father.
Then there's the idea that the Earth sits in this weird zone (the "Plural Z" sector of space) that leads to multiple Earths, multiple dimensions. This, too, shows a creative spark that could have been interesting to explore. Maybe Fenchurch had gone back to Earth after losing Arthur and the two of them could have gone world hopping, chasing each other until they found themselves again (with a teenage daughter they now had to raise). Considering Adams's creativity and wit, this could have been fodder for a really zesty adventure.
The problem with Mostly Harmless is that it's just so spiteful most of the time. It starts, of course, when it rips Fenchurch away from Arthur. Instead of actually exploring Arthur looking for her, going on a real adventure to get her back, the book more or less shrugs and just gives up on the two of them. Fenchurch, it should be noted, never shows up in this book again, and that's a real wound to the story. She'd been a great addition to the series and she brought out a spark in Arthur that this fifth book has no interest in reviving. She disappears and the book just wallows from there.
Random Dent doesn't help matters. Whatever was going on with Adams at the time, he wrote a nasty and obnoxious little girl that I seriously doubt anyone likes. Random has one mood, sullen rudeness, and she uses this at every turn. Considering that Random is in a good two-thirds of the book, and is the constant focus on Arthur, having her be such an awful character really ruins this whole section of the story. If Adams would have written some kind of hole in her armor, something that let a character we actually could like out through her defenses, that would have helped a lot. Sadly no.
Finally there's the end of the book. Once our heroes get to Earth we see the whole Vogon plan come to fruition (and spoilers for a 30-year-old book): the Guide 2.0 was an intelligent device that, once on Earth, found a way to merge all the various Earths together, creating a single world. With all the Earthlings -- Arthur, Random, and Trillian included -- on the planet, the Vogons then blow it up, finishing the job they started all the way back in The Hitchhiker's Guide to the Galaxy. And that's it, that's the end of the novel. Rocks fall, all die.
As an ending to the series it was incredibly unsatisfying. If Adams could have written a sixth novel then maybe this story would have been easier to accept. He could have found a way to write himself out of this, making it a cliffhanger instead of the end of the story. A Mostly Harmless, Part 2 (or, likely, he would have called it The Salmon of Doubt) would have helped to secure the legacy of the series, and redeem this book in the process. That didn't happen, though, and for twenty years Mostly Harmless stood as the end of the series.
That wasn't the true end, mind you, but it was the end of what fans could consider the "official" Hitchhiker's Guide. In 2009 a sixth book was released. It was authorized by Adams's widow and written by Eion Colfer. We'll cover that novel later and, yes, it does find a way to write the series out of the mess of Mostly Harmless. Still, it's hard to call it a true continuation, authorization of it. The writing isn't Adams's and it does feel off. For me, then, I prefer to think that the series ended at book four, So Long, and Thanks For All the Fish, as that book gives everyone in the series a proper, uncompromised ending. It's better that way.