Discovery of the Borrower Siblings

22 yr old Kate Felts lived in her boyfriend's, Brett, apartment, but when they break up, she moves in with her best friend's ,Willow Potts, apartment. She then later starts noticing weird stuff happening there.

Bella and Alec are borrowers that live in Willows walls in her apartment, Bella is 18 yrs old and Alec is 20 yrs old. They lived there for 8 years after their parents had died many years ago, the last thing Alec heard his mom say to them was "Keep your little sister safe".