Bode first discovers the key hidden in the garbage disposal at Keyhouse, and it is the second key he ever finds after the Anywhere Key. He asks Dodge — whom he wrongly believes to be on his side — what the key does, and she tells him that it allows the user to communicate with the dead. She entices him to show his mother, Nina.
Bode attempts to use the key to communicate with his father, Rendell, however, does not enter the mirror despite seeing his reflection. Instead, Nina enters the mirror and finds herself trapped. She tries to escape but finds herself surrounded by mirrors with no exit. Bode returns to the well to question what the key actually does, and Dodge reveals that the key is the perfect prison and that many have died trying to escape. He enlists Tyler and Kinsey's help to save their mother, and Tyler enters the mirror with a rope tied around his waist and pulls Nina from the mirror.
Nina does not remember the whole ordeal — due to the Riffel Rule, however, this is not stated — and Kinsey also believes the experience to have been a hallucination. Bode shows her the key in action the following day, however, and she is convinced that she did not imagine the whole thing, despite being told otherwise by Tyler.
The key, when inserted into a mirror, allows the user to open a doorway to a parallel-pocket universe. The user is then enticed to come into the mirror by their reflection and upon entering, they find themselves in a dark, empty abyss. Surrounded by mirrors and their own reflection, it is quite difficult for those trapped within the mirror to escape, and Dodge remarks that it is the perfect prison.
This key can also affect a mirror's reflection if it is held toward a mirror, as it makes the reflection eerily pleasant as if to beckon the person to enter the mirror.