A spacecraft burning toward a futuristic city.

Writing a single novel is hard enough, and writing an entire series is notoriously difficult. It’s so difficult that when I published a post on tips for writing sequels, some commenters responded with the equivalent of “don’t.” In particular, it’s a real challenge to maintain reader interest across multiple books. Some series jump the shark while trying to raise tension, as the stakes are already so high that it’s impossible to credibly raise them. Others forget to raise the stakes or add novelty, meandering around through the doldrums of boredom. You even see books that fail to have a real ending because the author thinks they need a cliffhanger to sell the next installment.

We have a post on planning a novel series, but this is a really complex topic, so it’s useful to examine how the pros do it. To that end, today we examine three book series that successfully kept their tension up and maintained interest, each in a different way. One is highly episodic, one strikes a balance, and one is a continuous story. It’s time to learn their secrets!

1. The Murderbot Diaries

An armored figure walking next to a multi-limbed robot.

Martha Wells’s excellent scifi series is mostly made up of novellas, but the lessons we can learn from it apply to novels as well. It’s the most episodic of our three examples, which is fitting since it so often invokes tropes from episodic TV shows.

How Each Book Builds on the Last

The first book has excellent tension from the first page. Murderbot, our protagonist, has to keep its human clients alive while also not giving away that it has free will. Normally, SecUnits* like Murderbot are denied free will, but our hero has hacked its governor module. From there, Murderbot has to protect its clients from hostile corporate rivals, all while maintaining the illusion that it’s a normal SecUnit. By the end, Murderbot’s humans are safe, and they’ve accepted it as a free agent.

Book two has Murderbot facing off against a different group of enemies that are actually weaker than the first book’s villains, which sounds like a letdown. However, Wells makes it work by having Murderbot lose access to most of its equipment, so it has a lot less firepower to work with. The emotional throughline here is Murderbot investigating an event from its past: it was told that years ago, it went rogue and killed people. By the end, the physical enemies are defeated, and Murderbot learns that it wasn’t responsible for the massacre after all, which furthers Murderbot’s arc of learning who it is.

Book three raises the external stakes by pitting Murderbot against a squadron of combat bots. While bots aren’t as quick thinking as SecUnits,* these are much more heavily armed than anything Murderbot has faced before. Emotionally, Murderbot has difficulty accepting that a friendly bot named Miki is genuinely fond of humans. To Murderbot, humans are either enemies or clients, no emotions involved. At least, so Murderbot says. By the end, it’s accepted that Miki’s friendship with humans is real and has gotten those humans to safety. This helps Murderbot accept that it has also formed friendships with humans.

It’s a good thing, too, because book four sees Murderbot ride to the rescue of its best friend, a human named Dr. Mensah, who’s been abducted by the bad guys from book one. Here, Wells further escalates the physical stakes by pitting Murderbot against a Combat SecUnit. This enemy has all of the combat bot’s firepower and all of Murderbot’s tactical genius. Not only is it incredibly satisfying to watch Murderbot vanquish such a foe, but the emotional payoff is great too. By the end, Murderbot has realized that it doesn’t need to wander the galaxy anymore, and instead goes to live with Mensah and its other human friends.

How This Maintains Interest

Wells’s most obvious tactic is increasing the physical danger in each book, either by denying Murderbot its usual resources, making the enemies stronger, or both. The stakes stay essentially the same: keep a group of humans alive, but tension still goes up because that’s harder to do each time.

More subtle are the emotional stakes. The series is highly episodic, with very little connection between most of the physical conflicts. That ensures a satisfying ending each time, because Wells is never tempted to end on a cliffhanger. However, it might also mean that no tension is left to pull us to read the next book. That’s where the emotional stakes come in.

Murderbot’s character arc is actually the series throughline. Murderbot starts off with no meaningful relationships, as it distrusts humans and disdains other AIs too much to make friends. Murderbot has legitimate reasons for this attitude, but it’s still a problem. By the end, not only is Murderbot more comfortable in its own skin, but it’s also formed a deep friendship with Dr. Mensah and a few other trustworthy humans. A beautiful character arc.

Incidentally, we can use these lessons to show why the follow-up novel, Network Effect, doesn’t work as well. First, the physical conflict doesn’t escalate. Murderbot’s enemies are actually far less capable than the Combat SecUnit from the last novella, and Murderbot also has additional allies. The stakes are the same as they’ve always been: keep a group of humans safe. Meanwhile, Murderbot’s emotional arc is nonexistent. It does make a few new friends, but that hurdle was already cleared, so it doesn’t mean as much. Network Effect would work fine as the first book in the series, but it’s seriously lacking for such a late installment.

2. The Expanse

A spaceship passing close to a chunk of ice.

The second entry on our list is James S. A. Corey’s space opera epic about economic inequality in a far-future solar system. Okay fine, it’s also about cool space battles and spooky alien tech. But mostly economic inequality. The first six Expanse books sit nicely at the midpoint of the episodic to continuous scale. They’re clearly part of the same story, but most of them stand fairly well on their own.

How Each Book Builds on the Last

The first thing Corey does is establish a volatile political situation. Earth and Mars are decades into a tense cold war, always looking for a way to one-up each other even though they’re ostensibly allies. Meanwhile, both inner planets exploit the Belt, a collective term for humanity’s many deep space settlements in the Asteroid Belt and beyond. Belters need medicine and food supplies from the inner planets to survive, and in return, Earth and Mars squeeze them for every last crumb of minerals they can mine.

Second, Corey adds alien tech called a “protomolecule” to stir things up. This is a kind of alien 3D printer. It can consume anything, including humans, to produce advanced alien tech. Books one and two are all about different factions trying to get their hands on the protomolecule while our heroes struggle to prevent civilian casualties. Both books end by preventing major loss of life and bringing the bad guys to justice for their protomolecule crimes. They’re more than a little similar, but Corey preserves novelty by giving book two’s baddies some government backing, rather than just being corporate stooges like in book one.

Book three changes the script by focusing mainly on diplomacy. The protomolecule has created an FTL jumpgate that links to thousands of uninhabited worlds, and naturally the major powers are one wrong move away from fighting over it. None of the previous villains reappear, but that’s fine because the political conflict that created them is still going strong. Our heroes’ mission to keep the peace is complicated by their sympathies for the Belters and by the protomolecule’s own inscrutable plans. By the end, the Belters have at least won a seat at the table, and the jumpgate is free for human use.

Book four is another left turn, as our heroes journey through the gate to mediate a dispute on one of the new colonies. Although this is far from home, the same conflicts persist. While the colony’s divisions aren’t entirely clear cut, it’s obvious that one side has far more Belters on it, along with poorer colonists from the inner planets. And of course, the alien ruins are always causing some kind of trouble. By the end, the good guys have forged an uneasy peace and figured out new ways of keeping alien tech off their backs.

Finally, books five and six come as a pair. A new villain arises from a splinter faction of Belters, someone with no qualms about mass murder in service of his political goals. His appearance is a bit sudden, as it seems like we’d have heard of such a capable leader before, but it helps that he’s still part of the same political conflict we’ve had since book one. It’s also questionable to make the big villain part of the marginalized group in your conflict, but we’ll discuss The Expanse’s politics some other time.

In a first for The Expanse, this bad guy not only sticks around for more than one book, but he actually wins at the end of book five, devastating Earth with an asteroid bombardment. Meanwhile, he’s been supplied with high-tech warships by mutinous Martian officers. Book six is all about putting together a coalition strong enough to take him down. That means getting the cooperation of a weakened Mars and stricken Earth, but it also means rallying other Belter factions. By the end, the bad guy is defeated and steps are taken to end the Belters’ marginalization once and for all.

How This Maintains Interest

In the first six Expanse books, Corey is a master of knowing when to raise the stakes and when to change the conflict. By the end of book two, our heroes have already defeated a Terran battle fleet, so continuing in that vein wouldn’t work well. There’s only so far you can escalate a space battle before the story loses credibility.

Instead, the story pivots to politics for a couple books, which keeps the conflict fresh. Book four also shows us an alien world, which is a great injection of novelty. The conflict is smaller scale than book three, which I normally wouldn’t recommend, but Corey pulls it off. Much like Wells in her second book, Corey gives his heroes fewer resources in their smaller conflict, so tension is maintained. Book four also spends a lot more time developing the individual colonists, and that attachment makes us care more about what happens to them.

In terms of continuity, the solar system itself is what links the stories together. In the early books, while each villain is self-contained, they all spring from the same political conflict. Readers are drawn back because they want to know what will happen to the solar system. Will the Belters finally win equality? Will Mars and Earth go to war? Which unscrupulous jerk is going to get their hands on the protomolecule next?

Finally, book five ratchets the tension up to eleven by handing the villain a big win: bombarding Earth and taking control of the outer solar system. Even though this is very much an open conflict by the end, Corey avoids making it a complete cliffhanger. Instead, the main question in book five’s later chapters is whether the heroes can even survive the aftermath of the villain’s attack. Defeating him isn’t on the table until book six.

Since book six has entirely resolved the setting’s main political conflict, that would have been a good place to end the series. But the protomolecule plot was still going, so Corey had to invent an entirely new political plot for later books. The new bad guys are certainly powerful, but since they don’t arise naturally from the setting, they feel less real, which lowers their threat level.

3. Legend

A black bird pattern on a blue background.

In our final entry, we look at the YA Legend trilogy by Marie Lu. This is a near-ish future dystopia where the oppressive Republic rules over roughly half of the modern United States, and most people must choose between starving in the streets or dying in a bloody war. It’s also the most continuous of our three examples; each book is clearly part of the same story.

How Each Book Builds on the Last

Book one establishes all of our major elements. We have the oppressive Republic and its war with another North American nation, the Colonies. Then we meet our two protagonists: June and Day. June is an elite military student from the upper crust, while Day is a street-smart thief who struggles to get by. Are they gonna fall in love? I bet they’re gonna fall in love. We also encounter some secondary plot elements, like Day’s brother Eden catching a deadly virus that occasionally sweeps through the Republic.

This book is mostly concerned with June and Day’s relationship. June is chasing Day because she thinks Day killed her brother. Meanwhile, Day is trying to rescue his brother after the government takes Eden away to run experiments on him. The two of them tangle several times, and it’s clearly an enemies-to-lovers story. By the end, they’re not quite at the lovers stage, but they’re at least working together. The big climax is June saving Day from execution, which is a satisfying end to the first book.

However, it’s clear that the larger story isn’t anywhere close to done. Day’s brother is still a prisoner, the Republic is still oppressive, and there’s still a war with the colonies. Book two picks up a short time later, and while the lovebirds’ relationship continues to develop, the primary external conflict is dealing with the Republic’s government. It turns out that one of the Republic’s new leaders is a devoted reformer, and our heroes decide to support him in the hopes of improving things. This provides plenty of political intrigue, and it also introduces some complication into the romance, as this young leader makes eyes at June.

Book two ends by defeating the Republic’s most conservative politicians, which at least puts the country on a path toward reform. Again, this is satisfying, but the story clearly isn’t done yet. There’s still a war going on, and the Colonies’ corporate overlords aren’t ready to make peace just because the Republic is treating its citizens better.

The final book is about ending the war, not through military might but by creating a cure for the virus that’s ravaging both nations. This is a pretty radical shift from where the trilogy started, as both our heroes are now fighting on behalf of a reformed Republic rather than against it. This is also where June and Day’s romance is finally concluded. By the end, our happy couple has saved the day, hooray!

The only downside is a bizarre epilogue in which Day loses his memory and goes to live on another continent. Hey, I don’t get it either – that’s just what happens.

How This Maintains Interest

Initially, Lu creates interest with traditional methods. Day is a likable character, so we don’t want him to get caught. June is also quite likable, so we’re worried that she might kill Day because she was lied to about his crimes. Then Lu builds the chemistry between the lovebirds, which creates more tension. We want them to get together, but we’re worried they won’t!

It’s after book one ends that Lu’s technique gets interesting. She leans hard on the series throughline to bring readers back for more: you can’t stop now – you have to learn what happens to the Republic and the war! In a lot of books, this method results in a story that doesn’t have an ending at all. It feels like you’ve reached the end of a chapter and the rest of the story is missing. Authors assume that readers will have no choice but to pick up the next book if they want to know what happens. However, it can actually drive readers away. Why should a reader trust that book two will have a satisfying conclusion when book one didn’t?

Lu avoids this problem. Sure, there’s a lot left to be resolved in the series, but she still resolves a major conflict in this book: whether Day will be executed or not. June and Day also reach a major milestone in their relationship: no longer being enemies. Lu repeats this trick at the end of book two. That time, she resolves the conflict over the Republic’s oppressive government but leaves the bigger war storyline open. In both cases, the open plots create tension for the next book, while enough is resolved to give each ending satisfaction.

Legend is as far toward the continuous end of the spectrum as a novel series can get without sacrificing the satisfaction of individual books. Its only major stumble in this area is the contrived amnesia plot at the end of book three, which I can only assume was to create tension for a fourth book that would be published a mere six years later. If that’s the case, then it was a bad plan.

To maintain interest over a long series, you need something that keeps readers coming back for more. It might be a high-stakes external conflict like Lu’s war story, or it might be a slow-burn internal conflict like Wells’s emotional arc. You might plan it in the outline or discover it as you revise, but it’s got to be there. Without something to connect the books together, there’s nothing to draw the readers back in. That’s how sequels get left on the shelf to gather dust.

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