"Behind You"

 Mark's phone buzzed with the text: "Turn around." He had been sitting alone in the coffee shop, his back to the glass window. Frozen, he dared himself to glance up into the reflection and saw only his own pale face.  Another buzz: "I see you." Mark bolted upright, scanning the room. Empty. Outside, rain blurred the streetlights. When he sat down again, his coffee had disappeared, replaced by a folded note. "I said... not to come.

"The doorbell clanged behind him. Mark turned and saw someone standing there, holding his coffee....