Launch days tend to be somewhat of a bittersweet occasion. You've done all you can for the book and it's now time to send it into the world and hope it finds its wings. That's not quite true, of course, as there is still plenty that can be done and that needs to be done for the book -- working on promotions, arranging giveaways, perhaps a book signing, and so forth. But mostly you've said good-bye to the characters, to the story.
That's even more the case when it's the last one in a series, as The Bellbottom Incident is; while there may be at least one short story to go along with the series, the three full length novels are done and it is time to clear the board and get cracking on that next idea.