After getting threatened again by Lila, Marinette is done letting herself be bullied and decides to expose the liar once and for all. She gains some unexpected friends and allies along the way.
Alternatively: Mari stops putting up with other people's bullshit and starts standing up for herself, debunking a liar along the way.
Seven didn't lie about only having cameras in the hallway of Rika's apartment, but he never mentioned having recorders in your bedroom. So when you were talking to Jaehee on your phone, he ends up finding out some interesting things about you. And he certainly plans on using them.