what happened in the first five minutes of bridesmaids?

Annie (Kristen Wiig) is a single woman in her mid 30s, living in Milwaukee. After her dream bakery, Cake Baby, failed, she lost her boyfriend and all of her savings, and now works in a jewelry store and is in a sexual relationship with the self-absorbed and married Ted. Her friendship with her childhood best friend Lillian is her only source of happiness.

When Lillian becomes engaged to her boyfriend, Doug, she asks Annie to be her maid of honor. Annie agrees, but is secretly concerned about how things will change. At the engagement party, Annie meets her fellow bridesmaids: Lillian's cynical cousin Rita, idealistic friend Becca, raunchy future sister-in-law Megan and Helen, the "perfect" wife of Doug's boss. Helen and Annie are immediately jealous of one another's friendship with Lillian. Driving home, Annie is pulled over by Officer Nathan Rhodes for having broken taillights. The two flirt, and he lets her off with a warning after discovering that she was the owner of Cake Baby, which he always enjoyed.

Annie's attempts to serve as the maid of honor go abysmally after she takes them to a seedy Brazilian restaurant that gives everyone violent food poisoning. Meanwhile, Helen, with her wealth and connections, constantly upstages Annie: rejecting Annie's idea of Parisian bridal shower, getting them access to a chic bridal-gown studio after Annie failed to make a reservation, and ordering expensive designer bridesmaids gowns for the group that are beyond Annie's means. Worried about her limited finances, Annie suggests a bachelorette party at Lillian's parents' lake house. Helen overrules her and books a trip to Las Vegas. Annie refuses to allow Helen to buy a first-class ticket for her and sits in economy class. Because Annie is afraid of flying, Helen gives her sedatives and alcohol, causing Annie to become inebriated and paranoid, and her outbursts force the plane to land in Casper, Wyoming, where the wedding party is escorted off the plane by police, canceling the Las Vegas bachelorette party. On the bus trip back to Milwaukee, Annie tries to apologize but Lillian quietly states that she wants Helen to take over planning the shower and wedding.

Distraught, Annie contacts Nathan and the two hang out while she discusses her difficulties. Nathan is sympathetic and encourages her to open a new bakery, but Annie refuses; her business' failure was so painful that she has given up baking entirely. After spending the night together, Nathan buys baking supplies, hoping to reignite her dream. This makes her uncomfortable and she abruptly leaves, breaking things off with him despite liking him. She is then fired from her job for lashing out at one of her customers and evicted from her apartment. With nowhere else to go, and her friendship with Lillian strained, she moves back in with her mother (Jill Clayburgh).

Attending the bridal shower, Annie discovers that Helen has created an elaborate version of Annie's Parisian theme, later upstaging Annie's heartfelt, handmade gift by giving Lillian a trip to Paris to be fitted for her wedding gown by one of the world's top designers. Annie snaps and throws a tantrum, destroying the decorations and food. Lillian kicks her out of the shower and disinvites her from the wedding. On the way home, Annie's unfixed taillights cause a crash and she is stranded. Nathan answers the emergency call, exasperated that she still has not fixed her taillights, and tells Annie how much she hurt him and not to contact him again. Annie calls Ted for a ride, but when he expects sexual favors for the drive, she dumps him and walks home.

Annie becomes reclusive, doing nothing but watch TV. Megan finds her and tells her to stop feeling sorry for herself with tough love. Annie realizes her errors and decides to make amends with Nathan, getting her taillights fixed and baking him a cake, but he appears to rebuff the gesture, leaving the cake outside his house. On the day of the wedding, Helen appears on her doorstep, begging for help in finding Lillian who has gone missing. In the car, Helen tearfully apologizes for all she has done to hurt Annie and explains how lonely she is: her husband is uncaring and she has no friends, suspecting that she is only invited to weddings for her party planning skills and connections.

Annie contacts Nathan, who begrudgingly helps them find Lillian hiding at her own apartment...