Anu (Sujatha) is a happy-go-lucky girl head-over-heels in love with her boyfriend Bharani (Ravi Kumar). Her life changes when her father gets transferred to Mumbai (then Bombay). Her love life falls apart as Bharani doesn't respond to any of her letters. In addition, her father becomes seriously ill. Her father's office colleague, Ramanathan (Rajinikanth), becomes a great source of strength for her in these tough times. Soon, he asks for her hand in marriage. She accepts gratefully, and confesses that she had a boyfriend, who has seemingly forgotten her.

However, Anu soon realises that Ramanathan is a sadistic and jealous husband, who tortures her no end. She opts for a divorce and, with an infant in her hands, she lands in Chennai (Madras) to take up a new job and start a new life.

Her life takes a turn for the better in Chennai as she has a very supportive friend-group in her office, particularly a widower, Janardhan (Kamal Haasan). Janardhan, or Johnnie as he is popularly called, is a talented ventriloquist who "talks" through his puppet, Junior. He falls in love with Anu, but is unable to muster up the courage to tell her about it.

In an interesting cinematic twist, Ramanathan's mother Leelavathi discovers that her son had married and tortured Anu and takes up a job as a maid in Anu's house to make atonement for her son's sins.

Anu also stumbles upon Bharani in Chennai and discovers that her letters to him never reached as they were intercepted by his mentally-challenged sister. Soon, Anu renews her relationship with Bharani and life seems to be looking up for her. But the ghosts of the past continue to haunt her. Ramanathan comes to Chennai in the role of her boss – a contrite and repentant Ramanathan, who now wants to remarry Anu and redress the wrongs he had done. The situation becomes piquant with 3 men vying for Anu – her ex-love, her ex-husband and a silent lover lurking on the sidelines.

• Sujatha as Anu
• Kamal Haasan as Janardhan (Johnny)
• Rajinikanth as Ramanathan
• Ravi Kumar as Bharani
• Leelavathi as Leelavathi
• Kumari Padmini as Rajathi
• Kutty Padmini as Gayathri

Kamal Haasan learnt the art of ventriloquism in order to portray his character perfectly. Both Haasan and Raghuram worked as choreographers for the film. The song "Junior Junior" was picturised on Haasan's character using a puppet named Junior.

The soundtrack was composed by M. S. Viswanathan and lyrics were written by Kannadasan.^[17] Viswanathan composed the song "Angum Ingum" within 15 minutes.^[18] The song is set in the carnatic raga known as Dheerasankarabharanam,^[19] while "Kaatrukkenna Veli" is set in Bala Nandhini.^[20]. Rediff wrote "K. Balachander once again shows his ability to use music as a narrative technique and the songs tuned by M. S. Viswanathan were all big hits, particularly "Kaatrukkenna Veli", "Junior" and "Angum Ingum".^[21]

In 2003, Rediff wrote, "A tad stagey by today's standards, this film still has much to recommend it".^[13] Four years later, Rediff wrote, "Avargal was considered a progressive and radical film by the seventies' standard. Rajnikanth gave a classic performance projecting a combination of two contrasting facets of villainy -- both openly sadistic and wily. He actually outdid himself as the wily scheming man".^[5] In 2011, after Balachander had been given the Dadasaheb Phalke Award, Rediff named it one of Balachander's best and wrote, "Avargal is yet another film that portrayed a strong female protagonist".^[22] A writer from The Hindu in 2011 commented about the film, "I emerged highly impressed. The characterisation was fascinating and the acting underplayed to perfection. There's the sadistic husband played to perfection by Rajnikant, the wife who walks out portrayed by Sujatha whose eloquent eyes mirrored pain even when she smiled and Kamal who mesmerised as a Malayali ventriloquist, silently admires Sujatha".^[23] Malathi Rangarajan of Hindu wrote: "Avargal is yet another film in which Sujatha scored a ton, despite the powerful presence of Rajinikanth, Kamal Haasan and Ravikumar" and also praised Rajni's performance as "one of his best till date".^[24] The Tamil magazine Ananda Vikatan, in a review dated 13 March 1977, appreciated the film, mentioned that it was a different attempt, and that though the film was narrated with many flashbacks, with Balachander's touches they were not a burden to follow.^[25]

• Filmfare Award for Best Actress – Tamil – Sujatha^[26]

The film is widely regarded as one of the finest that Balachander had directed.^[27] Baradwaj Rangan while analysing the dominance of female characters in Balachander's films included Avargal as one among them.^[9] Clips from Avargal were screened along with clips from other films such as Server Sundaram (1964), Iru Kodugal (1969), Arangetram (1973), Aval Oru Thodar Kathai (1974)and Azhagan (1991) at a function held in Balachander's honour at Tiruchirappalli in January 2015,^[28] a month after his death.^[29]