- Introduce new characters.
- Change narrative perspective.
The first one I believe is so as not to cheat the reader - for example: "I've been leading you along about Francis being the murderer; it was actually Johnny from down the road, a character who I haven't mentioned once before in my entire novel, but hell, he's as good as anyone to pin this confusing convoluted plot of a murder on and it fills those nasty plot holes I've managed to dig for myself."
It's a cop out and it's not fair. It's lazy, it's mean and it makes for a wholly unsatisfactory ending for the reader.
The second sin is less of a deal breaker, although it isn't necessarily good form and it stinks of poor writing and it is still kind of a cop out. You've written four fifths of the novel from Gary's perspective (third person, first person, whatever) and then you switch to Rodney's perspective in the last three chapters. Not only is it confusing for the reader, but it's also a bit disorientating and it messes with the flow. The readers have invested time with Gary, read about his thoughts and feelings, been there with him through the good and bad times, taken a journey with him. Now Rodney turns up, talking in your head, giving you his opinion. Who does this Rodney joker think he is, hijacking the narrative?
Grumpiness, followed by disconnection, followed by book in bin.
Hmmm, very sinful . . . .
Well, forgive me Father, for I have sinned. But hell, I think it works! I've committed the sins above but nowhere near the two-fingers-up-to-the-reader atrocities of the examples above. I definitely haven't cheated the reader. I still think the novel flows. But hey, time will tell.
And that time is fast approaching. As I type this, I only have four more scenes to write in the first draft of my novel. Exciting times and about time too. Saturday will be dedicated to those four scenes; Saturday night will be dedicated to celebrating.
I might just pop open some bubbly to celebrate or at least have one or two beers at the pub. I might let the hair down, go a bit wild. That's the exciting thing about sins, you never know which one you'll commit next. And there's loads of fun in the committing.