Complex sentence: Later the Green Goblin kidnaps Mary Jane after Harry Osborn's birthday party where Norman would have revealed Spider-Man's secret identity to everyone present, if Peter hadn't stopped them by creating a fire in the house.
Split into simpler sentences: Later the Green Goblin kidnaps Mary Jane after Harry Osborn's birthday party. There Norman would have revealed Spider-Man's secret identity to everyone present, but Peter stopped him by creating a fire in the house.