WARNING: MATURE CONTENT
Serena kept on walking, confident that he's following her while making sure that no one's behind them. Entering the school's main building, it was a little dark, but the huge windows provided some light in the shadows. She climbed up the stairs.
Charlton was walking behind her from a certain distance. He looked around to ensure that no one was following. Seeing Serena enter the main school building, he made a stop to check once more that no one's around. When he saw that it was safe, he went in to follow. He climbed the stairs and saw Serena waiting for him at the 2nd floor's landing. He was about to take double steps to get to her faster, but then, she used her right hand to signal him to stop. So, he did.