Five years after the original Pretty Little Liars series concluded its 160-episode run, the spin-off Pretty Little Liars: Original Sin premiered on Max, and their shared continuity poses a few interesting possibilities. The original series, inspired by Sara Shepards book series of the same name, follows four best friends from the town of Rosewood as they attempt to solve the mystery of their fifth friends kidnapping and uncover the secret identity of A, an anonymous source who threatens to reveal their darkest secrets. After seven successful seasons, the ABC Family/Freeform show ended in 2017.

https://screenrant.com/how-original-sin-is-connected-to-pretty-little-liars/