Teesri Kasam is based on Phanishwar Nath Renu's story 'Maare Gaye Gulfaam'. It centres around Heeraman, a bullock cart driver (Raj Kapoor) who is almost caught smuggling contraband, he vows that he will never smuggle. Heeraman is a simplistic man who gets taken in by people easily. Next he gets into an accident carrying bamboo and vows to never carry bamboo again. Thereafter, he is asked to transport a lady called Heerabai (Waheeda Rehman) from a nautanki company (Waheeda Rehman) to the village 'mela' which is quite far away. As she spends time with Heeraman, during the journey, an innocent rapport is built betweeen them. Iftekhar plays the young, flamboyant zamindar who lusts after Heerabai. In the end she is faced with a difficult choice. Life is a nautanki - can she play the role of Savitri for the rest of her life? The movie ends with the third vow that Heeraman has to take.