Don is a suspense action thriller about a street singer Vijay (Amitabh Bachchan) who is hired and trained by DCP D'Silva (Iftikhar) to take the place of a wanted criminal don who resembles him. D'Silva wants Vijay to gather all the info of don's syndicate and his illegal activities for his men believe that don is missing in action but has already been killed by the former in an encounter. Helping Vijay in his mission is Roma (Zeenat Aman) and JJ (Pran).