Complex sentence: When Kelli and Leigh descend to the garage to investigate, Melissa is attacked with a plastic bag before she escapes into her room, as she attempts to climb out the window the assailant throws a pair of ice skates, scalping her head.
Split into simpler sentences: When Kelli and Leigh descend to the garage to investigate, Melissa is attacked before she escapes into her room. As she attempts to climb out the window the assailant throws a pair of ice skates, scalping her head.