A bittersweet drama covering 30 years in the lives of group of friends united by their devotion to the theatre, 30 Ans begins in Paris in 1974, when Aurelian, his girlfriend Barbara, and childhood friend Antoine form a theatre. Taking the plight of Pinochet's oppressed Chile as its cause, the theatre attracts the involvement of Jeanne, a young actress who immediately sparks the attentions of both Aurelian and Antoine. When Chilean dissident actor Luis is brought to the theatre by Barbara's diplomat father, Jeanne falls in love with him, and the two carry out an affair that ends when a sudden development causes Jeanne to disappear. 8 years later, Aurelian has a new girlfriend and is directing a travelling troupe, and Antoine is a high-priced image consultant who gets his old friend a gig at Dunkirk. Aurelian, deeply immersed in a mid-life crisis, still loves Jeanne, continuing to carry a picture of the enigmatic actress in his wallet and writing about her in his diary.