Alya and the rest of her classmates walked to the alley where they were supposed to go. They had gotten another message from M saying to come meet her. They didn't know who she was, she wore makeup so they couldn't tell. (Yeah, and make up is so effective in hiding your face. Then again, this is Miraculous Ladybug characters we're talking about.) All they knew, was that she knew them and they knew her but they just don't remember.
If course Alya has her suspicions, she thought it was Chloé in a wig at the beginning because she didn't show up, but the next time they were ordered to meet the mysterious woman, Chloé had come saying that she was 'curious' but Alya had a strong feeling that Chloé was threatened into coming.
Anyone who could come up with a threat that scared Chloé and make her not tell her dad about it... well, that made Alya listen, because no one could scare Chloé except for M... whoever she was.