the broken heart

mystery

It was snowing outside!
Serah and mina was so excited about serah's 18 th birthday. Only a week to go.
Mina was busy texting to someone. Someone rang the bell.
  (some noise from outside was heard)
  Serah opened the door. It was a little boy. He gave a letter and ran away before she ask anything.
                 ***********************
In the letter nothing was written except a three digit number, 666.she closed the door and said this to mina. Mina was not listening as she was busy texting.
  Serah put on a woolen cloth and went outside. She went to a nearby park to spend time alone with herself. After reading that number, her mind kept repeating the number just like she know what that means.
  All of a sudden she ran and went to room number 666 which is near to her apartment room.
  She rang the bell. A old woman opened the door. After seeing serah she closed the door on her face. Serah knocked few times. She didn't know why she did that.
  Serah tried opening the door.The door was not closed. She went inside and asked, "why did you close the door?, i am here to ask something. "
  There was no sound. Serah asked"is anyone there? "
  She checked everywhere for that old woman. But she was not there. Serah start to sweat. If no one was there, then who opened the door?