Ann

In the dark garage area, take the key near the end and use it to open the locker. Complete the escape sequence. After you wake up from unconsciousness, pick up the key to the north, and continue up instead of towards the exit. Don't get caught during the next escape sequence until the very end(where you're moving super slow). Get through the maze, eventually ending up in the Principal's Office again. Interact with a box of files on the right hand side to find a telephone number, then use the telephone to call it. Then just let everything play out as scripted, and you'll unlock the achievement!