Thank You (2011)

Raj (Bobby Deol), Yogi (Suniel Shetty) and Vikram (Irrfan Khan) are best friends and business partners who are married to Sanjana (Sonam Kapoor), Maya (Celina Jaitley), and Shivani (Rimi Sen), respectively. What their wives don't know is that their husbands cheat on them often with not one, but many women.
Yogi has already been caught by Maya after the latter hired her new-found friend Kishan (Akshay Kumar), a private detective, to check on Yogi. Now Yogi's status in the marriage is reduced to that of a butler at home. Yet Yogi still has aspirations for more hanky panky if the right opportunity comes along.
Raj is in good shape, as Sanjana is quite gullible and suspects nothing. However, Sanjana finds out from Maya that the necklace that Raj had supposedly bought only for her actually was a buy one, get one free deal. So where is the other necklace? Shivani, Maya, and Sanjana all get together, and Maya decides to hire Kishan to tail Raj.
Kishan has built his reputation as a man who saves marriages by getting erring husbands to mend their ways, and is also an expert in playing the flute. When he is first introduced to Sanjana, he seems to fall in love at first sight, or so it is made to appear at this point in the film. Initially a sceptical Sanjana rebukes Kishan's early attempts to prove that her husband is a lying cheat. This, however, only makes Kishan more determined.
Kishan first attempts to bring all the girlfriends of Raj, Vikram and Yogi to one party, at the same time when all the wives are there as well, to force a surprise face-off, thus exposing the cheating husbands. But Raj, with the help of the others, manages to lie his way out of the situation convincingly. Frustrated, but now even more determined, Kishan hatches a new plan, to break the friendship of the three men, by portraying Yogi as a traitor.
Raj and Vikram, initially embarrassed, now become suspicious that someone is helping their wives behind the scenes, to ruin their marriages. They decide at this point to seek professional help and look to hire a private detective to find out who it is. In a twist of fate, they end up at Kishan's office! However, Kishan pretends he has no idea who they are, and chooses to play a double game, agreeing to act as their detective while unknown to them being the very person working for their wives that they are looking for.
Kishan now records Yogi talking to Sanjana in a park, hires a voice-over artist, and dubs the tape with Yogi now appearing (in the voice over) as if he is betraying Raj and Vikram's secrets to Sanjana. Kishan then shows this altered version to Raj and Vikram, making them to feel betrayed by Yogi. However, as fate has it, they get a chance for revenge right away when Yogi calls and confides in them that he is off to see Sweetie, one of his old girlfriends.
Raj and Vikram are quick to reveal this information to Maya, as a result of which Yogi is caught red-handed by Maya, who goes ballistic at the site of Yogi in a hotel room with a girlfriend. Kishan also manages to get Raj, catching him standing in his bathrobe outside an apartment building window ledge due to his girlfriend's husband unexpectedly showing up at the door inside. Kishan calls in the news channel and the police to get the stranded Raj broadcast live on TV. He then calls Sanjana, asking her to turn on the TV and see for herself what Raj is up to.
Caught red-handed, Raj asks Vikram for help, the later comes up with a ploy to make it appear that both Raj and Vikram are undercover police officers in real life. And as such, Raj was out on a mission when caught on camera and that the whole resulting "cheating husband outside window" scenario shown on TV was actually all a misunderstanding. The gullible Sanjana wholeheartedly buys into the story, much to Kishan's frustration.
Kishan now hatches his own counter-plot and pretends to be the gangster don, King (Mukesh Tiwari) who is supposedly out to kill Raj and Vikram, thinking they are indeed police officers. When Raj and Vikram come face to face with King, they quickly backtrack on their story of being undercover police officers. However, King (Kishan) is able to scare Raj and Vikram into being blindfolded and taken as his prisoners. He then has them admitting, unknowingly in front of Sanjana and Shivani, that the whole secret agent thing is a fabrication and they have many girlfriends with whom they cheat on their wives regularly.
Sanjana and Shivani become extremely upset upon hearing these confessions, the latter fainting on the spot and Sanjana attempting suicide soon thereafter. Meanwhile, the double agent ruse has begun to wear thin after all this time. While at his office, Raj, Vikram and Yogi accidentally figure out that Kishan is, in fact, the person behind all the troubles they are in with their wives. When Kishan arrives, they quickly surround him with the intent to harm him, when all of a sudden Sanjana walks in. She is quick to defend Kishan, who had earlier saved her from committing suicide. At this point Raj threatens to divorce Sanjana, mistakenly assuming she is in love with Kishan.
Sometime later, with the divorce finalised, Raj, Vikram and Yogi are found drunk at a lake-side restaurant, when Kishan appears all of a sudden. He has with him wedding cards inviting the three over to a wedding. Raj assumes its Kishan and Sanjana's wedding, and starts to chase after Kishan. Since he is drunk, he keeps missing and then accidentally smashes a police officer. The three friends are then arrested, and put in jail. Where they reminisce about the tragedy that has befallen them. But the next morning, they are bailed out by the don King, much to their surprise.
Out of jail, and armed with a gun supplied by King, Raj, full of rage, heads straight for the wedding and straight away shoots Kishan, supposedly killing him on the spot. However, it turns out, the bullets were all fake blanks, planted by don in collaboration with Kishan himself. Kishan gets up and reveals that the wedding was actually supposed to be between Sanjana and the surprise groom, Raj himself, much to the embarrassment of Raj.
It becomes clear at this point that Kishan was never after Sanjana herself as has been made to appear throughout the film. But that Kishan did all this because he himself once had a wife (Vidya Balan), who committed suicide after finding out that Kishan was cheating on her. From that day on, Kishan decided to become a private detective going around saving marriages in crisis, like his own. After this emotional revelation, Raj, Yogi and Vikram promise to give up outside-relationships. All the couples get back together, Raj and Sanjana get remarried. At the reception, Sanjana's sister asks Sanjana's mother where he is, Sanajana's mother says that he has gone to rescue another marriage in crisis. It then shows Kishan walking in town, playing his flute.