Headstrong 23-year-old guitarist Lilas Mayassi lives with her mom and younger brother on the outskirts of Beirut. By day, Lilas teaches music to kids. By night, she’s trying to keep her thrash-metal band Slave to Sirens together. She’s also secretly falling for a young woman living across the border in Syria. Growing up in the shadow of their parents’ civil war, Lilas and her bandmates — Shery, Maya, Alma, and Tatiana — have big dreams but few opportunities, until they’re invited to play Glastonbury, the world’s largest music festival. “Sirens” is a vibrant portrait of a young woman struggling to define herself in Lebanon, a region of the Middle East as complex as each of the Sirens themselves.