—¿Qué haces, Lu? —susurré al acercarme, tratando de disimular mi nerviosismo. —No es de tu incumbencia —respondió sin levantar la vista, concentrada en ajustar un objeto metálico que colgaba de su cintura.
First, I need to consider the context. The phrase "bajo la falda de mi prima" translates to "under my cousin's skirt." That image could be symbolic or literal. Since the user included "espionage" in the title, maybe the story is about a cousin wearing a skirt that hides something or someone. A common trope in espionage could be someone hiding a device or being a spy. espiando bajo la falda de mi prima
Start with a setting in a quiet town. Introduce the cousin as trustworthy but with a secret. The protagonist is curious and notices something strange. Maybe the cousin is preparing for a mission. The protagonist finds a device and is involved. Conflict arises, resolution. Make sure the story is for a younger audience, since espionage stories can be intense. Keep it lighthearted with a positive message about trust and discretion. —¿Qué haces, Lu