One of Terry Pratchett’s ongoing tricks with the Discworld has been ‘the idea whose time has come’. Some genius/evil force from the Dungeon Dimensions creates an oddly familiar invention and the population of the Discworld embrace it as though there was a hole in their experience and history and thinking that could only be filled by this new innovation.

As ever, Pratchett makes an excellent real-world point. There are some things which, once invented, are clearly things we’ve always needed, not just as useful items but as ways of thinking and doing.

Take that terribly simple innovation enabled by the internet: the book bonus feature.  Back in the day, either you finished the story and drew a line under it or you wrote another full book. Snippets and ideas, little plot threads that didn’t fit in a novel, backstory that wasn’t plot-relevant: it all had to lurk in a notebook, unwritten, unread, waiting for an academic to pick you for their PhD.  We the reader never got to find out what happened to that lovely pair of minor characters, or to see that offstage scene, or to find out where the hero had been before the book began – because none of that got written, or at least published.

And now, we can. In one of my favourite romances of the year, Glitterland, the hero makes a rather dramatic gesture. Because of the way the ending is staged, we never get to see the lover find out about this (which is structurally correct but a little agony for the reader).  Except now there’s a free bonus feature with a post-ending scene so we can see his reaction. You don’t have to read it at all if you’re a ‘just the book’ purist, or you can wallow in it if you’re all teary over Ash and Darien. (I wallowed.)

This is on my mind as I have been spending the last few weeks writing shorts set in the world of The Magpie Lord. There will be a little taste of my hero Crane’s backstory in China, and a story that takes place two days after the ending of book 1. There’s also a print exclusive story set after the end of book 2, with another of Stephen’s cases of magical crime.

These aren’t plot-crucial. There’s nothing that will spoil a reader’s enjoyment if they don’t see it. They’re just bonus features, a little treat for readers who enjoy the characters, to deepen and broaden the experience of Magpie-world. If I wrote in a period before the internet, when there was no reasonable way to put out a 5000-word short just to amuse readers of the previous book, I wouldn’t have written them.

Here’s a funny thing, though.

The print exclusive story is happening because book 2, A Case of Possession, is a bit too short for print. My publishers are not the sort of skanky people who just mess about with font size and margins to stretch the text. (I speak as exactly that skanky publisher. I once made a 35K word text fill a 50K print length. Shame, shame.) However, book 2 is dedicated to my best friend, who ruthlessly insisted on seeing her name in print. So my publishers agreed that I could write a special exclusive story to make it work, and I muttered under my breath about lousy rotten friends and set off to come up with a story.

And as I wrote this unexpected thing, without any plan to fit it into the main flow of the characters’ ongoing adventures, I quite suddenly learned something about one of my main characters, Merrick. Something huge. Something that shines a completely new light on his backstory, and his relationship with Crane. Something that clarifies a massive plot difficulty in Magpie 3, which I am currently writing, and turns everything on its head, and enables me to go down a plot path that I’d been fearing and resisting because, until I knew this fact, it simply didn’t quite work – and now it does.

Magpie 3 will work in a completely different way to my original plan because of what I learned about Merrick in this short story. I don’t know if I’d ever have learned that about him if I hadn’t written it. I find that rather scary.

How often did a character remain unilluminated, a plot unexplored, because there was no opportunity to tell readers the story, and so the author never found out for herself? There’s no way of telling. But I’m glad I live in the age of the bonus feature. They’re useful little buggers.

The Smuggler and the Warlord will be exclusively on the Blog of Sid Love from 2 December. Interlude with Tattoos will be a free download from Smashwords and Goodreads from 10 December. I will probably mention it when they go live.

Cover design by the fantastic Susan Lee

A Case of Possession will be out from Samhain 28 January 2014. I for one can’t wait.

Bonus features: do you love them, are you unexcited, or it is just evil modern nonsense?