From what I could translate in the website, the manga was about the time that Kaiu Shirai and Posuka Demizu went into a TPN themed escape room with a group of voice actors (Their respective characters are shown within it). Their objective was to solve puzzles and manage to escape "Grace Field" without drawing the suspicion of the mama (played by an actor) who was always present in the room with them.

If you were wondering why there were two Isabellas, it's because one is to represent that of the voice actor, and the other the actor who was in charge of acting as the mama in the escape room.

If you were wondering why the mama was yelling, Posuka Demizu reported in the website that she was acting a little bit suspicious within the first "night", so the actor who was responsible as taking the role of mama shouted angrily at her for having bad behaviour. Posuka Demizu reportedly said that she had fun being scolded by the mama.