Complex sentence: Clary isn't pleased and leaves the apartment to hang out with Simon, finding him at a poetry reading where she also runs into Jace, one of the demon hunters (called Shadowhunters or Nephilim).
Split into simpler sentences: Clary isn't pleased, and leaves the apartment to hang out with Simon. She finds him at a poetry reading, where she also runs into Jace, one of the demon hunters (called Shadowhunters or Nephilim).