Haydar Ali and Ceylan's relationship, which began with great passion, takes an irreversible turn one unexpected night, leaving Haydar Ali caught in the middle of both the state's secret plans and Istanbul's ruthless underground world. Ceylan, meanwhile, crosses her own boundaries to protect the man she loves, embarking on a dangerous journey along the fine line between innocence and guilt. In this world where betrayal, loyalty, and the instinct to survive are tested, a single misstep can have deadly consequences for everyone. The Underworld tells the story of a man's battle with fate and his own darkness in a universe where even love is subject to rules, with breathtaking suspense.