Even though I finished my trilogy over the summer, it wasn't until last month that I had people read over the complete set. The reactions were very favorable, but there was some discussion about what came next.
"Next?" I said. "This is it. It's a trilogy."
The reaction I got persuaded me that I had to do another book to tidy things up.
Thus, like Douglas Adams, it appears I will have a four-volume trilogy. I started working on it a couple of weeks ago and am about 20,000 words into it. Based on how the other books went, that is either a quarter to a third of the way through.
Of course, then it has to be reviewed, proofed and edited, and given that I'm a part-time author, it may be ready by the summer.
That's okay, because people haven't even seen the other two yet.
One thing's for certain: Book Four is really, really going to be the end. Seriously.