Plot Twist in Chapter 5

It think the biggest event is happening in Chapter 5. A new character Olivia, Lorenzo's half-sister, appears. Early of the chapter, a phone call starts to ring, and Lorenzo thinks it is mom so he picks up the phone with anger. However it is actually Olivia, his half-sister. Lorenzo, again, thinks it is a trap set by his mom so he tries to keep his real information from her. Surprisingly, she asks him not to tell about the phone call with her. The big thing finally happens when Lorenzo takes a nap. Someone is fiddling with the lock on the door. And Lorenzo, with feared, hides. Someone comes in his cellar and he is found pretty easily by someone. The identity of someone is revealed as Olivia. She doesn't seem like caring much about why Lorenzo is staying here. She is here for the box which seems pretty important to her. After she finds the box, she gets out of the cellar. In the night, she comes back again asking can you do me a favor; let her stay for a while.