Inscrutabilities Interpreted

This book contains four different mysterious thrillers in which the main theme is to solve a mystery. In this page, you can read the plot of each story

Sketchbook: the drawings in the book were drawn by the man's dead twin brother.
Mail: A girl in this story used to talk with a man who didn't exist.
Believe me: If someone opens the door when it was 3 times knocked, all the people in that room would die or be killed.
Plus 10: In this story, when people travelled in the bus, their age would get changed once they stepped out.

A point to be remembered is that all the stories are truly fictional and nothing is true except some simple facts.