1980s Dublin. A 14-year-old boy named Conor (Ferdia Walsh-Peelo) is looking for a break from a home strained by his parents’ relationship and money troubles, while trying to adjust to his new inner-city public school where the kids are rough and the teachers are rougher. When he meets the mysterious, über-cool and beautiful Raphina (Lucy Boynton), he aims to win her heart and invites her to star in his band’s music video. She agrees, but there’s only one problem: he’s not part of a band...yet. Now Conor must deliver what he’s promised. Calling himself “Cosmo” and immersing himself in the vibrant rock music trends of the decade, he forms a band with a few lads, and the group pours their heart into writing lyrics and shooting videos.