readers - What are the things to consider when writing a sequel to a novel from another author?

I am talking about writing a sequel to a novel that's in the public domain. For example, Wizard of Oz. As far as I know, this is completely legal; however, the issue is how to deal with the fandom that exists. There are things fans want to see in a sequel and things that would be blasphemous to them, so how should you navigate this? Any guideline or procedure? I am thinking Dune has a huge fandom, although I am not sure if Dune is in the public domain. I don't think it's would be a good move to start your writing career with a sequel of Dune, wouldn't it? You can use any franchise as an example (even if they're not in the public domain) in your answer.

Answer

IANAL but I definitely recommend verifying you're on legally safe ground, even if it means getting authorisation from an author or their estate, as with the example I'll discuss throughout the rest of this answer, which focuses on the writing side. Excluding franchises that were designed to have multiple authors such as The Hardy Boys, by far my favourite example of an author writing a sequel to another's work is Stephen Baxter's 1995 The Time Ships, an authorised centennial-marking sequel to The Time Machine by H. G. Wells.

If you've never read the original 35,000-word novella, do; just be warned it's hardly modern in its style. But read the sequel next. Baxter finds a way to believably step into those Victorian shoes without making the writing inaccessible to a 1990s audience. He takes what worked in the original (a premise he fleshes out in a much longer, more complex story that didn't feel padded even when I read it as a child), and eschews what wouldn't again (telling almost the entire story as a quotation; Wells technically used an irrelevant other character as the first person narrator). Baxter also explores many questions Wells didn't: how would history change once multiple time machines enter the picture, how do they work, and how was the first one built? This allows him to give us alternate twentieth-century events, rather than an 802,701 that's less relatable. I also liked the supporting Morlock, Nebogipfel, plus a number of other things I'd better not mention because the plot doesn't deserve me spoiling it.

I think the lesson to take from Baxter is you have to not only love the original and know why you do; you also have to know why it's loved in general, and what would make a fitting answer to that. But every work is different, so I can't say specifically what you'd need to do. If you do read Baxter, however, try to think about why his decisions were prudent (and won multiple awards!), and more importantly how he'd come to them.