I have remembered a middle-grade book (series?) that I'd read probably around 4th-6th grade. These are all the details I can remember:
- It was a medieval fantasy esque setting.
- It featured a world with some sort of king or dark lord that the protagonist was trying to defeat - for some reason, I don't remember why, this king was almost undefeatable. He could only be defeated by a secret word.
- Parts of the secret word were scattered around the land in syllables.
- The book begun with an ominous prologue in which a character had finally gathered all the parts of the word, and confronted the king - I think he might've been captured or something like that, and was brought before the king. When he said the word, it didn't work. I don't remember perfectly, but it might've been because the 'king' was an imposter, staged there to make the person say it and then the real king would come out.
- After saying the word, the person who said it immediately forgets it.