Complex sentence: Samantha and Courtney return to the adjacent house and retrieve the van keys; as they are about to leave, Samantha sees the killer outside, leading the two to retreat to a bedroom upstairs, where the killer attacks them.
Split into simpler sentences: Samantha and Courtney return to the adjacent house and retrieve the van keys. As they are about to leave, Samantha sees the killer coming toward the house, and the two retreat to a bedroom upstairs to hide, but the killer finds and attacks them.