Watch Heartthrob Full Movie Free Online 123Movies. Sam Maddox, a troubled girl whose father committed suicide, has earned a reputation at her high school for being a bit promiscuous. When Sam begins seeing brilliant, MIT-bound Henry Sinclair, the two opposites really attract. Although Sam doesn't realize it, Henry is in the grip of an insane romantic obsession, and he will kill anyone who tries to put an end to his star-crossed - and increasingly deadly - romance.