There are some situations that give us chills. Being stalked is one of them.
Imagine watching a movie in which the protagonist has a questionable person following him. The stalker jumps in and out of shadows, leaves clues and seems to be everywhere at once.
The protagonist is so terrified that he cannot function normally. The police are trying to help, but they cannot be everywhere at all times.
So far nothing untoward has happened, but the threat that something awful could occur occupies your character’s mind. It’s a dangerous situation, one that inhabits the mind and constricts behavior.
Your task is to write a story in which your character is being stalked. Begin small. It might be that the stalked looks familiar, or has a voice that reminds your character of someone he knows. It might seem accidental that the stalker keeps popping up, but when the quantity of appearances increases, then it gets just plain spooky.
Description will be important as you set the scene. In fact, each time that your character changes setting, new descriptions will be important. Dialogue will pop up when your character tries to tell someone what’s happening. Will the someone believe or not? Will the someone take action or not?
Have fun with this one.