Complex sentence: Assisted by her brother Nate, Casey finds a Houston memorabilia store related to the pin, but upon meeting the two owners, Hugo and Ursula, Casey is questioned about it, and when she says she knows nothing else about it, they attack her.
Split into simpler sentences: Assisted by her brother Nate, Casey finds a Houston memorabilia store related to the pin. Upon meeting the two owners, Hugo and Ursula, Casey is questioned about it, and when she says she knows nothing else about it, they attack her.