How about something along the lines of:
When a teenager using his psychic powers to score with girls accidentally tunes into the mind of a psychopath who fantasizes torturing and killing one, he must find and stop him before he acts it out.
Okay, not less than 30 words. ?But not more than 40 either. ?Anyway, given that the essence of a character arc is to go from a negative valence to a positive one, it would be better if the kid starts out squandering his psychic abilities on selfish pursuits. ?Maybe his psychic powers have newly emerged with puberty; he's like a kid playing with a new toy (negative). ?His character arc would be to grow up and use them as a tool for selfless good (positive).
So initially he uses his gifts to do foolish things like cheat on tests (by reading the mind of the nerd in the next row) and score with girls. And then he tunes into the brain waves of someone who likewise wants to score with girls --- in the worst possible way. ? He is able to visualize the psychopath's fantasies.
And then--worse--he begins to feel?the erotic desire underscoring the sadistic fantasy. ?That's the psychopath invading his mind, tapping into the inner, latent psychopathology in his own unconscious -- aka: his Shadow, for those who dig the depth psychology of CG Jung.
fwiw