Complex sentence: Lord Voldemort returned to the Riddle house with Peter Pettigrew, where he murdered Frank Bryce and organized the Triwizard Cup to be a portkey to the local churchyard, where he planned to kill Harry Potter in order to regenerate his body.
Split into simpler sentences: Lord Voldemort returned to the Riddle house with Peter Pettigrew, where he murdered Frank Bryce and enchanted the Triwizard Cup to be a Portkey to the local churchyard. He planned to kill Harry Potter there in order to regenerate his body.