I'm working on a novel that will have at least three distinct sections in three distinct locations (the two main characters start in the first location, travel through the second location, and one stays in the third location). I have an overall story arc that connects the whole narrative, and I think there are strong storylines for each location.
The problem is that the sections feel very different in tone, and stakes, and I'm worried that the book will feel disconnected and episodic. There's no single villain in the book --the main characters are the only ones who travel from place to place, although there are connections between the locations. The story for the first section is more of an action/thriller. The middle section has some action, but is largely about a love triangle. The last section doesn't have as clear a genre, but the overall book is conceived of as a coming-of-age story. There's also elements of a quest narrative and a mystery plot.
I know --that's a lot! My tendency as a writer is to overthink and overcomplicate things. I don't want to get lost in the outlining here, my goal is just to tell the strongest possible story with these characters and these settings. I've thought about just focusing on one section of the story, but I don't think it really has resonance without the rest. I've also thought about going non-linear, with flashbacks and so forth, but I don't want to confuse or lose the reader. How can I give this story a strong throughline that will keep it from feeling episodic?