When a restrained and reserved young FBI agent finds himself leading an investigation into a spate of violent, unsolved crimes spiraling out of control, he must unify the team, or risk demotion.

But when it’s revealed that high ranking members of the Spanish police maybe behind the city’s chaos, he must go undercover to bring about justice before his hometown is ripped apart.

“blind boy” = protagonist
“helps police identify and apprehend a possessed serial killer” = inciting incident
“must prove he witnessed the crimes” = main character goal

Seems the playfulness of this logline, might be the contrast of blindness vs. sight. How a blind individual’s witness of a crime would probably provide less useable evidence. But how this might link to a demonic entity, as the real homicide culprit, is the real challenge.

An important quality of story, is for the audience to first empathise with the main character. Tell us a little about the boy, not just his blindness, but one or two words describing his psychology. Courageous, weak, adventurous, timid … these are relatable qualities. That determine how he might relate to inciting incident events. That affect how he might emotionally respond to main goal struggles.