Having written a story over a million words long twice, I thought I'd sit down and do a brain dump of what I've learned about writing really long-form fiction—in the hope that it'll be useful to someone else who's just starting out on this ultra-marathon.

Now, a decade later, I've written a whole lot more. The Merchant Princes/Empire Games sequence is now up to nine books (yes, "Invisible Sun" is in the edit pipeline: it'll be published in March 2020). The Laundry Files is up to ten books, plus nearly another book's worth of short stories. (That tenth novel isn't announced yet, but will probably show up in 2020.)

So, about a decade ago I wrote an essay on this blog about the writing of the Merchant Princes series (at that point, six slim novels—the Empire Games follow-on trilogy wasn't more than a daydream back then), in which I tried to pin down what I'd learned about writing a series.

The first thing to understand is the scale of the task. Each of these projects, the Laundry Files and the Merchant Princes, represents a sunk cost of many years of full time labour. At my rate of production (roughly 1.5 novels per year, long term, where a novel is on the order of 100-120,000 words) either of them would be a 7 year slog, even if I worked at them full time to the exclusion of all other work. So we're talking a PhD level of project scale here, or larger.

In reality, I didn't work at either series full-time. They only account for two thirds of my novel-length fiction output: in the case of both series, I've gone multiple years at a time without touching them. Burnout is a very real thing in most creative industries, and if you work for a duration of years to decades on a single project you will experience periods of deep existential nausea and dread at the mere thought of even looking at the thing you just spent the last five years of your life on. It will pass, eventually, but in the meantime? Try not to put all your eggs in the one ultra-maxi-giant sized basket.

Burnout can be aggravated by external factors (deadline pressure, a deteriorating relationship with your editor(s), real life events such as a death or serious illness in the family), and in my experience the only guaranteed cure for it is some serious down time—either a writing sabbatical if you can afford one, or to work on a different project for a while (preferably one with none of the causes of stress: e.g. if stressed due to deadline pressure, renegotiate the deadlines then spend some time working on something that has no set delivery date, so that if it stalls out you won't be guilt-tripping over it).

The second thing to understand is the commercial constraints.

On the one hand, publishers marketing departments love a series: if I hand in a new Laundry Files or Merchant Princes book, my editor knows exactly how to tell the marketing folks to sell it. Publishers (If you write a successful novel, the first thing your editor will say is "write me another just like it, only different".) Readers often like long series works too: if they liked book 1 enough to plough through book 2 a certain proportion will buy every subsequent book in that series you write (unless and until you keel over and start typing GORILLA GORILLA GORILLA instead of keeping the ball rolling). Predictability is a negotiable but valuable commodity.

However, planned ultra-long-form works of fiction are murdered by market forces just a couple of books in.

This isn't just true of novels, it's true of comic books and TV shows too. Audiences are fickle. Sales (or readership, or audience size) tend to drop by 15-25% from episode 1 to episode 2, and keep declining exponentially. This isn't a sign that the project is bad, this is normal: consider, if you will, how many trilogies you've started to read, finished the first volume of, and then ignored book two (or got a couple of chapters in, then gave up). In some cases the decline is much steeper—30-40% from episode to episode: I speak from experience. This isn't just theoretical: it's why there won't be a third book in the series beginning with "Saturn's Children" and "Neptune's Brood": they sold okay in the USA, but then I changed US publisher—and the British sales took a 40% dive between book 1 and book 2, so I couldn't fall back on the UK market.

A series where the sales figures of book n are the same as book n-1, n-2 .. 1 are flat is worth persisting with, because it's bucking the market trend and not stagnating. And a series where the sales figures actually grow from book to book is a prize beyond compare.

Anyway, one point I'd like to hammer home is that the Merchant Princes and the Laundry Files are both survivors; drawing conclusions from them alone is therefore to some extent an exercise in confirmation bias. I have a number of other potential series works that succumbed along the way. I don't think I've ever started a novel without leaving open the possibility of there being one or more sequels. But many novels never get the sequel they deserve, and many sequels founder on the shoals of diminishing sales before they can spawn a series.

For example, consider "Glasshouse": it was shortlisted for a Hugo, but turned out to be my slowest-selling SF title in the US market so didn't get even a single sequel—'d have had to accept a reduced advance payment for the book, i.e. a cut in income. (One cited reason is that the book takes a weird turn about 20% of the way in; a more likely reason is that Ace tried for am abstract, "literary" cover design that didn't attract either my core SF readers or a lit-fic audience.) (NB: I had a title in mind for a sequel, but eventually decided to re-use the title on something completely different, so when "Ghost Engine" eventually turns up, don't mistake it for a sequel to "Glasshouse".)

This is why you see so many trilogies from new authors that end with book 2. The publisher welcomes them with a two book contract to lock them in, but cuts the trilogy off at the knees if sales of book 2 are down on book 1: if they buy a third book they risk throwing good money after bad. Which is problematic: while many readers won't touch a trilogy or series until it's finished, having been burned, the best way to ensure that it will never be finished is to not buy each book in publication month—because that causes the sales figures to decline!

A third point: if you plan a series in advance, it will deviate from the plan, sooner or later (and usually sooner). I drafted a four book series plan for the Merchant Princes in 2002, assuming that it'd be possible to publish it as a series of 600-800 page doorsteps. (Commercial reality then intervened, in the shape of sewing machine costs.) The Empire Games trilogy is what the third book in that series became, over a 15 year period—it bears little or no resemblance to the original pitch, and the fourth book in the original pitch will probably never get written because the actually-existing series has diverged too far from the original plan.

And indeed, if you try to stick too rigidly to the plan you'll damage your own work. A map is intrinsically less complex and complete than the territory it describes, and as you explore your new world in fiction you'll make discoveries that demand further exploration. New characters will turn up, new plot opportunities will suggest themselves, and you need to be able to adapt and extend your original design as it becomes more complex—then work out ways to prune it so that the complexity remains humanly manageable.

Another problem with writing a really long series is the human ageing process. I am not now the same Charlie Stross who wrote "The Atrocity Archive" in 1999-2000, or "The Family Trade" in 2002. I'm 17-20 years older than that guy. I am middle-aged, with middle-aged memory issues and middle-aged personality changes and middle-aged perspectives on life. I might, at a stretch, be able to parody my younger self's writing style and interests, but I don't really want to write about the same things now that I was writing about back then. So the original series plan may no longer even be appealing or interesting to you if you try to stick to it religiously—you need to be able to redesign your project on the fly, taking into account the already-published books that are already set in stone, if only by layering new interpretations of old story elements on them.

In hindsight, I got two things very right early in the Laundry Files: I made sure that Bob was flagged as an unreliable narrator, and gave him new understandings of the significance of older stories as the series went on. And I had Bob age by a year for every year of wall-clock time that elapsed during the writing of the series, at least up until 2015 (the year in which the Lovecraftian Singularity takes place in the Laundry Files). This allowed me to grow Bob as a character and the setting in terms of complexity, retaining my own interest in the series and making it more layered and nuanced as it went along.

The Merchant Princes developed rather differently. The first six-book series were written mostly between 2002 and 2006, although the last book ("The Trade of Queens") only came out in 2009. It was set in 2002-03, but not our 2002-2003. I then substantially re-edited it for a UK release, before continuing the series with a sequel trilogy, "Empire Games", set in the 2020 of that universe. (The original plan was for "Empire Games" to be published in 2015, but various factors delayed it, so that instead of surfacing as edgy near-future SF it's arriving as a strange kind of alternate present SF.) Again, by resetting the chronology by nearly a generation I was able to sunset some characters and introduce new ones—and also to rejoin a bunch of established ones at a later stage in their lives, allowing for personal growth and a change in the direction of the plot, from relatively naive action-adventure to complex realpolitik.

Anyway, here are some rules of thumb for writing ultra-long-form fiction:

The first couple of books should be stand-alone, or at least deliver plot closure for the readers, because it's possible the series will end early, for reasons beyond your control.

Don't even think about writing a series unless you're in love with it at a conceptual and character level, because if you get a working series off the ground, it will be with you for longer than the average marriage. As for writing two million-word series in parallel? That's just crazy. Or maybe it's polygamy. I'm not sure: I just wish I hadn't gotten over-ambitious in my thirties.

If the series doesn't end, you will burn out, probably several times, over the process of writing ten novels. Plan for it, and factor in taking years out to do something else while you get your mojo back.

You will become a different person while you work on your project, and this new you will be interested in different aspects of the story to the ones that held your attention in your youth. Give yourself permission to tear up and rewrite your series plan at will, otherwise you'll create a rod for your own back. If you haven't been through them yet, don't underestimate the impact of cognitive and other personality changes that will essentially turn you into a collaborator with your younger self.

It really helps if you allow your characters to age and change with you, and their understanding of the setting. (If not, well, that works for some writers too.)

Changing viewpoint characters within the series can also shake things up. (As witness the Laundry Files. It's all Bob for the first five books: thereafter, only one of the next five books is about Bob. Although Bob will probably return in book 11 or 12 ...)

It really helps to plan to prune plot threads and protagonists every few books. (Hint: the Red Wedding in "Game of Thrones", or the air raid at the end of "The Trade of Queens".) Middle-aged memory decline is totally a thing, and you ought to plan for it! (If I start any more Merchant Princes books after "Invisible Sun" they will, of necessity, be written as stand-alone novels in the same setting rather than a continuation of the earlier trilogy and series.)

Try to keep in mind a possible one-book series climax, even if you think it's going to take another five books to get there in practice? Just in case you get a terminal diagnosis. (If nothing else, your heirs will probably raise a toast to your memory, for the extra bump in sales that the final volume triggers as readers who've been holding off finally buy the now-complete series.)

As for where my two mammoth series are going ... the current plan (remember: all plans are provisional!) is that "Invisible Sun" ends the "Merchant Princes" sequence, second series. There may be standalone novels in the same setting eventually, but no definite plans for the next 2-3 years: I need a break from it. The Laundry Files main story arc should wrap up in another 2-3 novels (after "The Labyrinth Index"), but there are also side-quests: the tenth novel will probably be one of those, that is, a stand-alone story set in the same universe but not dealing with the Laundry or the New Management directly.

Any questions?