Enredo

A young social outcast in Australia steals money from her parents to finance a vacation where she hopes to find happiness, and perhaps love.

Muriel finds life in Porpoise Spit, Australia dull and spends her days alone in her room listening to ABBA and dreaming of her wedding day. A slight problem is she never had a date. Then she steals some money to go on a tropical vacation, meets a wacky friend, changes her name to Mariel, and turns her world upside down.—Lynn Salmon

Living in Porpoise Spit, Australia, twenty-two year old Muriel Heslop is a socially awkward (she unfashionably and unabashedly listens to ABBA music), slightly overweight, directionless woman with few life or professional skills. Her lack of self-esteem is fostered by the constant verbal abuse directed at her - and at her siblings - by their politician father, who blames whatever political problems he has on his family, who he deems to be a public embarrassment to him. Muriel's self-esteem takes a further blow when her so-called friends - the popular girls from high school - exclude her from their social circle. Muriel resorts to theft to make herself happy. Her life changes when she runs into another colleague from high school, Rhonda Epinstock. Also not in the popular social circle in high school, Rhonda is now a gregarious, carefree girl who can see Muriel's desire for an equally carefree life. The two move to Sydney together. Out from under the direct criticism of her father, Muriel feels that she can now put behind her all the problems of "Muriel Heslop", even changing her name to Mariel to escape those problems. She also feels she can now achieve true happiness, her primary goal being to get married. Despite continuing problems with her family and a new serious issue with Rhonda, Muriel seizes on what she sees as an opportunity to achieve her primary goal. But a further issue with her family makes Muriel finally come to the realization of what is truly important in her life.—Huggo

In the small coastal town of Porpoise Split, Australia, Muriel Heslop is a young, aimless woman and an out and proud ABBA fan, who wants to get married, which is made all the more difficult because of her abusive and domineering father. When she meets the quirky Rhonda Epinstalk, she steals money to fund a vacation, changes her name to Mariel, and turns her world upside down.—Tom Daly

Muriel Heslop (Toni Collette) is a high school dropout with no job, no prospects and no boyfriend. She uses fantasies of her wedding as a coping mechanism and also strongly matches the diagnostic criteria for a cluster-b personality disorder (possibly Borderline Personality Disorder or Histrionic Personality Disorder). In high School she was shy and socially awkward, but managed somehow to have the "in group" accept her hanging around them. Muriel attends the wedding of one her high school associates in an inappropriate leopard print dress. After witnessing the groom having sex with one of the bridesmaids, Muriel is arrested because by some strange coincidence the store detective from where she shop-lifted was also at the wedding.

After this episode, her former friends (Tania, Nicole and Janine) shun Muriel because they see her as an overweight, directionless no-hoper, while continuing to plan a holiday to Hibiscus Island. Muriel's chain-smoking, unambitious, slovenly family is routinely abused and vilified by their father - the corrupt local politician Bill Heslop (Bill Hunter). Frustrated with his family's lack of ambition or drive he has turned into a tyrant.

While at dinner with some property developers, Heslop runs into his mistress who has done well in a cosmetics pyramid marketing scheme who recruits Muriel into the scheme. The following day Muriel's mother writes a blank cheque to cash intending for the money to let Muriel buy into the scheme. Escalating from petty theft, Muriel uses the blank cheque to defraud her parents, draining their bank account of $12,000. Muriel uses this money to stalk her former friends on Hibiscus Island.

While on the Island, Muriel's former friends confront her over her stalking, requesting that she leave them alone. Later in the evening, Muriel runs into Rhonda Epinstock (Rachel Griffiths). Rhonda confronts Muriel's former social-group who bullied her in high-school. Rhonda and Muriel catch up, with Muriel inventing grandiose fantasies of a fiancé. Later, Rhonda and Muriel perform an Abba lip-sync in the talent contest. It is unclear where they got their elaborate costumes.

At the end of her holiday, Muriel returns home to be confronted by her mother over the fraud, however Muriel immediately moves to Sydney where she shares a flat with Rhonda and changes her name to Muriel. One night, Rhonda and Muriel go to a nightclub. Rhonda meets two American sailors while Muriel takes a nice man, Brice Nobes, she met at her minimum wage job in a video store. They return separately to the small flat that Muriel and Rhonda share. While engaged in rough foreplay, Muriel and her companion break a window. The sailors that were in Rhonda's bedroom go out to investigate and assume that Muriel's companion is attempting to rape her. It is during this episode that Rhonda falls down and apparently paralysed.

While waiting overnight in the only empty emergency room in Sydney, Muriel calls her family home where she learns that the Australian Federal Police are investigating her father for corruption. Rhonda discovers she has cancer pressing on her spine and requires urgent surgery. Muriel then co-opts Rhonda's health crisis as the basis of a deception to obtain a free photo shoot from a Bridal shop. During one of Rhonda's rehab sessions, Muriel promises that she will take care of Rhonda and that they will never need to return to their hometown. Rhonda discovers that Muriel has tried on every wedding dress in Sydney and confronts her. Muriel confesses the depth of her deceptions.

Bill and Muriel go to lunch with Bill's solicitors, where Bill confronts Muriel over her criminal fraud and Muriel confronts Bill about his infidelity.

Rhonda's tumour returns necessitating more severe surgery making her paralysis permanent. No longer wanting to be bothered with her only true friend's disability, Muriel moves out, leaving Rhonda no option but to ask her mother to take her back to their Porpoise Spit. Muriel enters into a criminal conspiracy to commit visa fraud marrying South African swimmer David Van Arkle so that he can stay in Australia. Muriel agrees to marry David for $10,000.

At Muriel's elaborate wedding, her former friend group serve as the bridesmaids, while Rhonda bound to her wheelchair is relegated to being a guest, which leads to an awkward discussion between Rhonda and her former bullies. Muriel's father is accompanied by his mistress and Muriel's mother arrives late to the wedding, missing the actual ceremony.

At the end of the ceremony, Muriel doesn't notice her mother at the back of the church and just walks past. After the ceremony Muriel and David return to David's apartment who gives her a perfunctory tour of place. After showing her bedroom to Muriel, David makes his contempt for Muriel known asking "what kind of person marries someone they don't know?" to which she replies "you did". He shows her a grudging respect when she says that she too wants to win. Realising that their marriage will be platonic, Muriel sits on her bed and contemplates the view.

Meanwhile, back in Porpoise Spit, Muriel's mother accidentally shot-lifts a pair of sandals from a supermarket. Bill arranges with the police for the charges to disappear and takes Muriel's mother home where he announces his intention to divorce Betty and marry his mistress, Deidre Chambers.

Betty commits suicide, although bill calls in favours to have it recorded as a heart-attack. Realising that Betty lived only for her family and that her constant marginalisation broke Betty's will to live, Muriel breaks down and realises that all the frauds, falsehoods and lies only lead to pain. David comforts Muriel and they consummate their marriage.

In her mourning Muriel realises that she can move beyond her family-of-origin issues, that her actions have consequences and that her choices matter. The next morning Muriel asks David for a divorce, who has decided that he likes having her around. However, she leaves him at the hotel wishing him good luck for in the games.

Bill asks Muriel to stay and help raise the kids; she refuses and returns to Sydney. She repays $5,000 of the $12,000 she stole, saying that she will repay the rest when she gets a job back in Sydney.

Muriel visits Rhonda at her mother's house and offers to take her back Sydney. Rhonda accepts.