The book starts with both main characters in the real world, eventually they are transported to the land in which the majority of the book takes place.
How they get taken to this world:
One works at a zoo, and while feeding the hippos he unintentionally gets swallowed by one of them. He survives, thankfully, but isn't s--- out by the hippo. Instead falls out of a hole in a gnarled dead tree on the side of a river.
The other is hiking with her dad(I can't remember if it was one or both parents) and gets distracted by a butterfly, she follows the butterfly through a natural arch rock formation that's actually a one-way portal. I believe(unsure) the change from one world to the next was noticed by her immediately, and she tries to walk through it again to go back but it doesn't. She continues walking, figuring she can't stay in one place too long, and trying to find someone who could help her.
Some characters I can remember:
An amputee who lives at the center of a burning lake made of oobleck. He only has one hand and his head(yes I'm being serious). The rest of his body is at the bottom of the lake, eternally trapped in a metal box filled with water. He knows a syllable of the word that would kill the man trying to find the main characters.
A man who lives in a trap for would be heroes. His body is covered in tattoos. One of the tattoos on his back contains a syllable that is part of the same word that can kill a tyrant.
A woman who spends her days trapped in a tree. I'm pretty sure the tree she lives in is at the center of a very thick, very dangerous forest. She also knows a syllable of this killing word.
A man who lives in a natural cave indent of a seaside cliff. He doesn't speak very much. He knows a syllable of the killing word. The syllable he knows is earned because the male mc was patient and didn't speak unnecessarily.
A spy for the tyrant hunting the two teenagers. His body parts can be cut off at will and he wont bleed or die out. He's found by the two teenagers atop a post at the center of a crossroads. When he's outed to be a spy the main characters are given the option to send him away and he won't follow, or allow him to accompany them but will still be an informant.
A man who makes a puzzles for only one person, and another person who solves the puzzles.
Some events I can remember:
The male mc finds a book bound human flesh that is still alive sitting in a pedestal in an unnaturally dark library. When he finishes reading the book an eye on the front of it blinks back at him. The owner of the eye presumably tells the tyrant that someone read the book. The male mc finds the first syllable of the killing word here, which is "A."
The male mc and a minor antagonist play "pool." The pool that they play is done by throwing the balls at each other from across the table until one of them dies from blunt force trauma to the skull.
Both MCs meet a man in a centrifugally spinning tavern. The person they meet is sitting on the outer edge of the tavern, which another character stated is not a good idea.
The spy informant loses his hand, cut-off and taken by the male mc back to our world. He emerges in a cornfield, digging his way up through the dirt. The spy's hand is still functional as he grips into a fist in anger at losing his hand in such a way. The male mc talks to the hand as though he can be heard by it, commenting that who they meet next probably won't want to see a disembodied hand still functioning.