There are, very roughly, two types of series. First, there’s the on-going arc, where the end of one story feeds into the start of the next and it’s necessary to experience the individual books in order. Examples of this would be The Hunger Games or The Wheel Of Time. Then there’s the ‘adventure of the week’ series, where a character (or cast of characters) take part in a new adventure in each story. Lots of mystery and detective series have this format‌—‌think Inspector Morse, Miss Marple, Jack Reacher. Series like these don’t need to be experienced in order, because each story is a stand-alone.

Of course, there are variations. An ‘adventure of the week’ series might include character arcs and story arcs that slowly develop over several stories (an example might be The X-FIles). An on-going arc series might include side-stories that exist as their own thing (think of the relationship between Rogue One and Solo, and the rest of the Star Wars films).

But in any series, there is usually some kind of continuity, in character, story and style.

Style? Yes. It’s important. Expectations set in one book shouldn’t be cast aside in the next.

Let’s take Star Wars as an example. The first film is full of action. If the sequel had focused on political machinations within the rebellion, with action played out predominantly off-screen, fans of the first would feel betrayed. Another example‌—‌imagine how readers would feel if a new Jack Reacher book turned out to be a slapstick farce, or had Reacher battling aliens. Or what if a new Hercule Poirot story portrayed him as an action hero fighting terrorists?

For a series to satisfy fans, it can’t afford to stray too far from the promises and expectations set in the opening.

Of course, there are always story-tellers who take risks. Think of the Alien franchise‌—‌the original film was a claustrophobic horror, whereas the second was a military action film. But there were enough similarities‌—‌enough continuity‌—‌for fans of the first to accept and enjoy the second.

I was reminded of this when reading John Scalzi’s Old Man’s War series. If I understand things correctly, this started off as a stand-alone book (Old Man’s War), became a trilogy, and then grew into a six-book series. What I find fascinating is how Scalzi makes each book different yet still managed to tell an over-riding story.

The first book is a military adventure, following the 75-year-old John Perry as he is given a new body and becomes a soldier for the Colonial Defense Force. But the second book, The Ghost Brigades, is a mystery story, and only mentions Perry a couple of times. It still follows on from events in the first book, and is still written in a similar style, but there are many differences between the two books.

Scalzi took a big risk here. If readers of the first book wanted more of Perry, they’d be disappointed. A fan of the military aspects of Old Man’s War could feel let down by the change of focus in The Ghost Brigades.

And in the third book, The Last Colony, Scalzi changes things up again. Perry returns as the main character, but now he’s leading a new colony, and the story focuses on the politics involved in his new role. Again, same story universe, different type of story.

But it works. There’s an over-riding arc to this trilogy, a through-story that binds them together.

Scalzi, from his notes at the end of the third book, intended to stop the series at this point. But he received questions about certain aspects of The Last Colony, and he wrote a fourth book. This is Zoe’s Tale. Again, he took a fresh approach. Zoe’s Tale is a retelling of The Last Colony, but from the point of view of Perry’s adopted daughter.

While I admire Scalzi for pushing himself here, I have to admit that this book didn’t work for me. Reading it straight after The Last Colony, the repetition of events bored me. Yes, there are a couple of new sequences, both important to the overall story, but that only covers about fifty pages. I also wasn’t convinced by his portrayal of the teenage girl.

This is only my personal opinion. Reviews suggest that others love Zoe’s Tale. But it was with trepidation that I started on the next book, The Human Division.

And I think this might be my favourite of the series.

Once again, Scalzi takes a different approach. By now, the overarching story has grown from that initial old man’s tale, and it now encompasses many planets and hundreds of alien species. The story is epic. But rather than write an ‘epic’, Scalzi focuses in on tiny details.

He does this by using short stories. Yes, the fifth book in the series is a collection of shorts. But they’re all tightly connected. They’re chronological, and they fit together like a jigsaw.

Scalzi could have combined all these stories into a single multi-faceted narrative, but I don’t think it would have worked. Some of the slighter arcs would have become lost. And the sheer fun in some of these tales would have been lost if they’d been mixed in with all the serious stuff.

The final book, The End Of All Things, uses a similar idea, but this time the book consists of four connected novellas. And it works very well‌—‌the novellas are long enough to sink into, and when taken together they give a fitting conclusion to the larger story.

Could Scalzi have written Old Man’s War as a straight-forward narrative? Possibly. Would it have been better or worse that way? I don’t know. Even in his serious moments, there’s a playfulness about Scalzi’s writing, and the changes in story style throughout this series are another aspect of that playfulness. He’s one of those authors whose willingness to try new things is a part of the appeal. Fans pick up a new book unsure what to expect. If it’s too similar to something he’s done before, they’re likely to be disappointed.

Which means this approach to writing a series wouldn’t work for every author. But it works for Scalzi. And it serves as an example that writers don’t have to stick to what is expected. Yes, experimentation doesn’t always work‌—‌but when it does, it gives something far more memorable than anything ‘safe’.