Igby and his older brother, Oliver, are are in the process of killing their terminally ill mother. His parents snipe at each other endlessly until his father tries to commit suicide and is sent to a mental hospital. Igby grows into a rebellious youth, gets kicked out of several boarding schools and ends up in a military academy. As Igby gets drawn further into the mind games and hypocrisy of the adult world, his already jaded outlook grows even darker. Ultimately, though, Mimi's impending death draws him back into the family fold for unexpected revelations and realizations.