DSP Shiv Kumar (Sunil Dutt) returns home to his wife Sheetal (Raakhee) and their young daughter and announces that he has been transferred to Bombay. Shiv Kumar has two brothers, Vijay (Amitabh Bachchan) and Ravi (Shashi Kapoor), who live in Mumbai. They are intelligent, capable guys but spend their time loafing about the city and swindling unsuspecting people. After resuming his work in Mumbai, however, a mystery man (Shatrughan Sinha) tries to assassinate Shiv Kumar. Shiv survives both the times.
Vijay and Ravi team up with Chacha (Johnny Walker) and Renu (Bindiya Goswami) who are a similar swindler pair. Vijay meets Sunita (Parveen Babi), yet another fraudster, during one of their adventures. One of their tricks eventually backfires and lands Vijay and Ravi in jail. Shiv bails them out and reads them the riot act at home. After the two attempts on his life, Vijay and Ravi advise him to find a different line of work, arguing that his profession is unpredictable, dangerous and unsuitable for a family man. Shiv stands firm, citing his undying patriotic commitment to his corps and his country.
The film introduces Shakaal (Kulbhushan Kharbanda). Shakaal is an international crimelord. (The character and his hideout are very closely modeled on the James Bond villain Blofeld and his headquarters.) He operates from a remote island outside India. Shakaal is a sadistic villain, who rejoices in pain of his enemies and traitors. Shiv Kumar gets progressively closer to the root of the crimes in the city. Shakaal has Shiv Kumar brought before him. He compliments Shiv on his wits and valour, and offers him to come to the other side. True to his form, Shiv Kumar firmly refuses the offer.
Shakaal tries to kill him, but Shiv breaks loose and tries to escape from the island. Shakaal unleashes wild dogs upon Shiv and eventually shoots him dead upon the beach. As Vijay, Ravi and Sheetal lament their tragic loss, the mysterious man who tried to kill Shiv shows up. Sheetal angrily identifies him. The man introduces himself as Rakesh, a marksman and former circus performer who used to shoot targets blindfolded (by sound). He was recruited by Shakaal to assassinate Shiv Kumar, by keeping Rakesh?s wife hostage.
Rakesh deliberately missed Shiv on the two previous instances, hoping it would buy him time to rescue his wife. On realizing this, an angry Shakaal killed his wife. Rakesh sought out Ravi and Vijay so they could work together to bring down Shakaal. The trio seek the aid of a homeless cripple, Abdul (Mazhar Khan in his first movie appearance). Abdul is a beggar who is also the man-who-knows-the-city. With Abdul?s help, the trio manage to find and destroy Shakaal?s contraband hideouts in the city. Enraged, Shakaal kidnaps Sheetal and has her brought to his island.
Vijay, Ravi and Rakesh fume, knowing that Sheetal will almost certainly be killed and that they have no clue about the location of Shakaal?s island. At this point, Jagmohan (Mac Mohan), another of Shakaal?s aides who has been mercilessly crippled by him, offers his help to the group to gain entry in Shakaal?s hideout.
Posing as a musical troupe, Vijay and Ravi (with Renu, Chacha and Sunita) enter the island and perform for Shakaal. Shakaal, however, reveals that Jagmohan was deliberately sent by him to trap them. Jagmohan?s fracture was a lie. Their cover is blown and they are secured. In an elaborate chase-action sequence as the three brave men escape, avoid the booby traps and henchmen, capture Shakaal and ultimately end him. Finally, the island is blown up and the heroes escape via helicopter to safety.