Complex sentence: Unbeknownst to Trish, however, Bill is a pedophile who is obsessed with 11-year-old Johnny Grasso, a classmate of their son, Billy.
Split into simpler sentences: Unbeknownst to Trish, however, Bill is a pedophile. He develops an obsession with 11-year-old Johnny Grasso, a classmate of his son, Billy.