Simply put, I already have the next two books planned out in my mind, and an idea for the fifth. I haven't written anything down yet, so it's all liable to change at my very fickle will. Without spoiling anything, books three and four will tell separate stories over the course of the same time period. Three will involve Dr. Malevolent and an attempt to take over the world, while four will tell a Captain Rescue story.
The Dr. Malevolent book will probably be similar to the first two books in style, only it will be sans a certain hero while he is off on his own adventure. That's really all I'll say about book two, since I don't want to give anything away.
I kind of want to do something a little different for book four, but not too different. I still want it to feel like it fits in the universe. That said, it's going to be a hardboiled/noir parody in which Captain Rescue will be flying (mostly) solo, trying to solve a series of kidnappings to the best of his ability.
Since I plan for the two books to take place during the same time period, there will be little references to each other and fun little nods. At first I was tempted to co-release them as two "book threes", but I think that might just confuse readers, and, for reasons I will not state here (!), I think it's better if the Dr. Malevolent story is book three and the Captain Rescue one is book four.
Anyway, the fruition of that multi book dream is probably a ways away. For the time being, I'm going to continue focusing on polishing Past, Future, & Present Danger for release sometime soon. Keep your ears and eyes peeled!