What is East Wall?

The House of Night is surrounded by a wall. Near the east wall, Zoey thinks she sees the ghosts of two fledglings that recently died from the Change. One night, Zoey also sees Loren Blake standing near the wall composing a haiku. Another night, Zoey sees Neferet meeting with one of the dead fledglings, Elliott. The east wall also has a trapdoor that leads on and off the school grounds.