Complex sentence: The Composer is Dead is an upcoming book written by Lemony Snicket (a.k.a. Daniel Handler), based on an orchestral performance for which Snicket wrote and performed the narration and Nathaniel Stookey wrote the music.
Split into simpler sentences: The Composer is Dead is an upcoming book written by Daniel Handler under the pseudonym Lemony Snicket. The book is based upon an orchestral performance for which Snicket wrote and performed the narration, while Nathaniel Stookey wrote the music.