You or your character has a secret admirer. How do you know this? What do you do to find out who it is? Do you find out? How are you changed by this?
Character
Think about both the person who is admired and the admirer. What do you know about them physically, intellectually and emotionally? What is their personality like? What is their greatest fear and what is their greatest desire? What do they want and what do they need? You probably know about both characters. The admired person doesn’t know about the admirer, but they admirer does know about the admired.
Story
What happens first? How does the story build? Think of perhaps three growing complexities. How is the admiration expressed? Is it pleasant or sinister for the admired person? How do things come to a head? What does the protagonist do about it?
Will your story have au upbeat or dark ending?
Form
Will you write a story, script or poem? Or has this actually happened to you? Can you write a piece of memoir?
You can also turn it all on its head and write the story from the point of view of the admirer. Or could you show both points of view?