So in my fantasy novel-thing, I plan on having the main character's older brother join the villain's cause. He left to join the army early in the first book (which i'm still working on), and the next time we see him he's already a key member of the villain's force. Originally I was going to explain through some flashbacks during the fight, but as I thought about it, I thought that it would be more effective for his decent into evil to be a story along with the MC's story. But I'm unsure because I feel like that it might take away the reader's attention from MC's journey throughout the story. Also if I do make it a sub-plot/side-story, it loses all shock-value for the reader I think. (Although who ISN'T expecting a member of the MC's family to be a bad guy, is the real question) Anyway I'm still not really sure. Any advice/suggestions?
Sounds like it would make a suitable sub-plot, nicely mirroring the MC's journey. That said, flashbacks would probably work well too...
You could do it either way, but something you might want to consider is how relevant to the overall story the specifics of the older brother's journey are. If all that really matters is that he turns evil, it might be best to play it as a reveal later and demonstrate it with a few short flashbacks; whereas if the brother's encounters with other characters or events during that time are important towards the main plot then it could be worth cutting to his perspective every so often. Alternatively, you could use his POV to show the reader key events that occur away from the MC or viewing the same events from a different perspective to add more depth to the story, even if the older brother himself isn't as important a character.
It could be a very nice sub-plot. I would suggest that you look at your story again, however, and see if it has room to do this plot justice. If you do decide to go down this route then it could change the direction of your story somewhat. It is, I feel, a more interesting concept to explore two brothers differing paths to meet their destiny and a lot of tension can be pulled from the two of them very nearly encountering one another several times, but just missing each other. I think if you weave that in to your story the chances are it will make it a more interesting book. You're writing fantasy so I assume your story, at some point, is taking the 'heroes journey' approach. As tried and tested as this is, there is no harm in putting a spin on that in order to make your book more interesting to the reader who, lets face it, will have read many other stories with the same structure.
A number of Civil War novels have families splitting allegiance, so brothers end up fighting on opposite sides. It can be particularly successful if you can represent both sides as devoted to defensible moral positions. In other words, try not to think of the opposition as "bad guys" even if your story is strongly slanted toward one side's position.
I think that it, in all honestly, depends on how important the older brother's journey is to the MC's journey. If the older brother's actions, at the time he does them, play a distinct role in how the MC acts, the stories should be side by side. But, I think it would also be rather effective if the MC didn't know the older brother was allying himself with the "bad side" so that both the reader and the MC are surprised. Then again, it's not good to completely throw the reader off guard, so there might need to be some hints in the story. But it all depends, I think, on the role the older brother plays in the MC's life and if the older brother's journey to the "bad side" affects the MC's development as a character. And I agree completely with Cogito's last statement about the "good side" and the "bad side." I can't think of a single conflict where each side didn't have some platform. Sides are generally made because of moral, political, ethical, racial, or religious dichotomies. And because of this, each side has a defensible platform that the true members of each side believe in. So, whether or not your story defines one side as "good" and one side as "bad," the members of each side need to be fighting for what they think is right. I think that was a bit of a digression and made very little sense.
maby you could do a two in one book where you show the mc's side of the story and then the sc's side.
Who says we need shock value, anyway? I think surprising the audience is overrated. While you lose that, you gain emotional tension by having the betrayal known.
Hmm... the question actually reminds me of one particular series I've read where this happens. The series I'm talking about is The Sword of Truth series, by Terry Goodkind. I think there's only one chapter that's devoted to showing what happens with Michael (Richard's brother..Richard is the MC). Goodkind writes in 3rd person omniscient so switches viewpoints chapter to chapter. I personally wouldn't use flashbacks unless absolutely necessary (I hate flashbacks in fantasy novels and very few of the ones I've read actually use them) and if the older brother's story is strong enough, then it may be that you could turn his story into one book and your MC's into another. Kinda like how Orson Scott Card did Ender's Game and Ender's Shadow (one is Ender's story and the other is Bean's story). Just my thoughts. ~Lynn