Reckless by Cornelia Funke

Reckless by Cornelia Funke, is a suspenseful story that keeps the reader on the edge of their seat. It starts off with a twelve year old boy whose father disappeared. His name is Jacob Reckless, and he has a younger brother named Will. Jacob discovers that the mirror in his father's study is a portal to a parallel world. This world is filled with magical creatures, and is very different from it's neighbor. 
Twelve years later, Jacob, who is now a grown man, has made a name for himself in the Mirrorworld as a treasure hunter. His brother followed him through this time and has been bitten by a Goyl. Goyl are people made of stone that wish to conquer the Mirrorworld. 
Jacob knows that he has limited time before Will grows stone skin of his own and becomes one of the fierce creatures. He goes on an adventure that will test his mentally and physically.
The Characters:
Jacob is very brave and clever, and probably the best treasure hunter in the world. He is restless, and needs to be on an adventure. Otherwise he will be miserable. Many girls are attracted to Jacob, yet he has never really stayed with one long.
Will's last name does not suit him at all. Where Jacob is rough, Will is gentle. Where Jacob is fidgety, Will is still. In love with a girl named Clara. Because of his sweet personality, the transformation is shocking when Will starts to behave like a Goyl: angry and fierce. He believes in Jacob.
Fox is a vixen that has the ability to change back into human form. She has been with Jacob since he saved her from a fox trap. No one can lie to Fox, and she knows Jacob better than he knows himself. She is secretly in love with Jacob, but the reader only finds this out later on, when there is an obvious connection between Jacob and Clara.
Clara is in love with Will, but later on, her emotions are clouded. Jacob and her both went for a drink at the river, but it turned out to be magical water. The water makes the drinker kiss and fall in love with the closest living thing, no matter how ugly. However, while Jacob continues to love Clara, she stays by Will's side always.
The relationships between these characters makes the book even more interesting.