In 1985, 16-year-old high school student Theodore "Ted" Stroehmann (Ben Stiller) is about to go on a prom date with his dream girl Mary Jensen (Cameron Diaz). Mary was supposed to go with her boyfriend Woogie. ted stands up when a bully manhandles Mary's dumb brother Warren, and Mary befriends him. She asks him to be her date for Prom. Mary lives with Charlie, Mary's stepfather (Keith David) & Sheila Jensen (Markie Post), Mary's motherTed he gets his scrotum stuck in his zipper (Ted was taking a leak and the bathroom window opened right in front of Mary's room and she thinks Ted was masturbating to her. Ted panics) & is hospitalized after managing to painfully unzip it, which cancels their date. Ted subsequently loses contact with Mary. School ended a few days later and her dad transferred to Florida.Thirteen years later in 1998, 29-year-old Ted is still in love with Mary. On the advice of his best friend Dom (Chris Elliott) (who is married), Ted hires private investigator Pat Healy (Matt Dillon) to track her down. Healy works with Sully (Jeffrey Tambor), who is in the Miami Police department, to track Mary. Healy discovers that she is an orthopedic surgeon living in Miami, and spending time with her friends and her neighbor Magda (Lin Shaye). After observing her for a few days, Healy falls in love with Mary. Healy learns that Mary wants a self employed guy like an architect to settle down with, someone who drinks beer and no drugs.. Wants to honeymoon in Nepal. Brenda (Sarah Silverman) is Mary's sarcastic best friend.. Her friends are perplexed that Mary has rejected perfectly good guys like Brett.. Apparently Tucker (who we learn later is Mary's patient) told Mary that Brett told him, that he would have proposed to Mary if not for Warren..He returns to Providence and lies to Ted about Mary, telling him that she is overweight and has four kids by three different men. Healy quits his job and returns to Miami to pursue her. He resorts to lying, cheating, and stalking to win Mary over. He says he has been to Nepal, and is an architect, and loves golfing, works with retards. They spend several weeks dating before Mary's friend Tucker (Lee Evans), a British architect who uses crutches due to serious spine damage, exposes him as a fraud. Healy is enraged after eavesdropping on Tucker, who lies about Healy not being an architect.Healy has a remote listening device which he uses to eavesdrop on Mary and Magda. He knows that Magda listens in on cellphone conversations in a 500 m radius. So he calls Sully with a script and admits that he is lying. That he is really is a peace corps activist who is very poor and works in third world countries to elevate poverty.. He says he didn't want to use his credentials as a currency with Mary.. Mary is impressed and takes Healy back.Meanwhile, Ted finds out from one of his old classmates that Healy was lying about Mary. He then drives down to Florida to see her. During the drive down, Ted picks up a hitchhiker (Harland Williams) who turns out to be a mass murderer (The hitchhiker kept talking to Ted about launching a video of 7 minute abs). The murderer leaves a body in Ted's car when Ted is unintentionally caught with a group of gay men while he tries to urinate.Ted is mistakenly arrested for the murder and bailed out by his friend Dom after the police catch the real killer. After Ted finds Mary (he finds Healy kissing Mary. although secretly Mary is not too convinced by Healy's attitude towards the "retards" which borders on harassment), they begin dating. Just after Ted meets Mary, Tucker tells her that Healy is a mass murderer and has a police record in Boston. Mary is horrified and breaks all contact with Healy. Healy was once again eavesdropping on Mary, and hears everything and is enraged..After subsequently tailing Tucker, Healy discovers him to be a fraud himself: he is an able-bodied American pizza delivery boy named Norm Phipps, who is also in love with Mary. Years earlier, Norm intentionally injured himself in order to get close to Mary, hoping that she would take him on as a patient. Although his injury has long since healed, he pretends to be disabled in order to gain Mary's sympathy, and he uses his friendship with her as a ploy to drive away any potential romantic rivals. Ted seems to have won her love until an anonymous letter exposes his connection with Pat, and she breaks contact with him.Ted confronts Pat and Norm, and Mary is accosted by Dom, who is revealed to be her ex-boyfriend "Woogie", whom she has a restraining order against, and was the one who sent the letter. He wants to reconnect with her as well, which she quickly refuses, so he tries to steal her shoes to satisfy his shoe fetish. Meanwhile Ted learns that norm (as Tucker) said lies to Mary about Brett, and Brett never said any mean things about Warren.Ted, Norm, and Pat arrive, and, when Mary is finally together with all of her deceitful suitors, Ted realizes that the only one who did not resort to lying or manipulation to win over Mary was an ex-boyfriend named Brett, who he learns is National Football League quarterback Brett Favre. Norm had previously confessed to Ted that he lied to Mary about Brett insulting her brother Warren (W. Earl Brown) (who lives with an intellectual disability), which was why she ended the relationship. After reuniting Brett and Mary, Ted leaves tearfully until Mary catches up to Ted, saying "I'd be happiest with you". Mary and Ted kiss while singer/songwriter Jonathan Richman, who has periodically narrated the story in song throughout the film, is accidentally shot by Magda's boyfriend, who was trying to shoot Ted as he was also infatuated with Mary.