Simon Spier, 17, did not tell anybody in his entourage that he was gay. He is in the last year of high school and thinks it would be better to keep this secret. One day, a young anonymous reveals Simon’s secret to the school’s blog. Simon decides to begin to correspond with him to find out who he is. Everything goes on the wheel until the day when another student discovers the mail and threatens Simon to reveal to everyone his secret. The teenager must prepare to face them all.