The story is about two friends and cops, Javed (Jackie Shroff) and Arun (Shahrukh Khan), who are both Special Task Force officers and partners.

Javed is a widower who is bringing up his 4 children with a lot of love and effort while Arun is his carefree, hotheaded, trigger happy albeit well-meaning subordinate and brother-like friend.

In a routine raid and bust operation, Javed and Arun lay their hands on the notorious drug lord, KKV (Nirmal Pandey) with the help of Inspector Sawant (Raj Zutshi). Later in court, KKV walks away using his powerful connections.

While on a subsequent drug raid, Javed is shot down by an unknown assailant - shortly after revealed to possibly be a rogue officer within the Special Forces department. According to the killer's hairstyle, it's obvious that the killer's actually Sawant. Arun's devastated and realizes that Javed left his four kids behind in his care in his will.

The kids, though, all dislike him at first but then grow to like him a lot. Arun then meets a housekeeper Geeta (Juhi Chawla) who develops a close relationship with the kids on account of also having had a close almost brother sister like personal rapport with Javed when he was alive.

Meanwhile, Arun continues the case to hunt down the killer who took his best friends life along with Sawant. Things take a dramatic turn when Arun sees a girl resembling Geeta dancing in a nightclub with the prime suspect in Javed's murder. At first unable to come to terms with what he has stumbled on.. He loses his temper at the children and creates a furore.

A few days later, it is revealed Geeta was an undercover agent for the secret police, who testifies against Arun in court and makes the judge believe he is a drug dealer. Geeta gets him suspended. With no hope left, Arun uses his own skills to find Javed's murderer. Arun realizes that JD's corrupted. When Arun goes to JD's residence, JD was already murdered. KKV, Chief, & JD are partners in crime. KKV kills the Chief. The police destroys KKV's henchmen. KKV's about to reveal that Javed's killer's name, but Sawant shoots KKV & Sawant lies to Arun that KKV killed Javed. Arun, Geeta, & Javed's kids mistakenly believe that KKV killed Javed. KKV reveals that Sawant killed Javed. Sawant finally kills KKV. Sawant also killed JD. Sawant killed Javed, so he could take his post a Senior Task Force officer. Sawant shoots Arun, but Arun's still alive. Javed's children manages to pull a rope, so a hard object can fall onto Sawant's head & Arun manages to beat up Sawant in a funny way. Arun kills Sawant. The film ends with Arun and Geeta together looking after Javed's children.

• Shahrukh Khan as Arun Verma
• Juhi Chawla as Geeta Choudhary
• Jackie Shroff as Javed Abbas
• Nirmal Pandey as Krishan Kant Virmani (KKV)
• Dilip Joshi as Champak
• Raj Zutshi as Inspector Sawant
• Akash Khurana as Commissioner
• Keith Stevenson as Chief
• Sahila Chadda as Bipasha
• Suresh Chatwal as Inspector Rajendra
• Madhur Mittal
• Fatima Sana Shaikh
• M. Rehman Naushad Ali as Broker

A. R. Rahman composed the soundtrack of the film, and lyrics were written by Majrooh Sultanpuri and Mehboob.

One 2 Ka 4 grossed ?11.20 crore (US$1.7 million) in India and $565,000 (?2.62 crore) in other countries, for a worldwide total of ?13.82 crore (US$2.1 million), against its ?12 crore (US$1.8 million) budget. It had a worldwide opening weekend of ?4.89 crore (US$730,000), and grossed ?8.01 crore (US$1.2 million) in its first week. It is the 21st-highest-grossing film of 2001 worldwide.

India

It opened on Friday, 30 March 2001, across 260 screens, and earned ?77 lakh (US$110,000) nett on its opening day. It grossed ?2.14 crore (US$320,000) nett in its opening weekend, and had a first week of ?3.71 crore (US$550,000) nett. The film earned a total of ?6.63 crore (US$990,000) nett, and was declared "Below Average" by Box Office India.^[2] It is the 20th-highest-grossing film of 2001 in India.^[5]

Overseas

It had an opening weekend of $275,000 (?1.27 crore) and went on to gross $375,000 (?1.74 crore) in its first week. The film earned a total of $565,000 (?2.62 crore) at the end of its theatrical run.^[2] Overseas, It is the 12th-highest-grossing film of 2001.^[6]