The film was partially based on a true story and subsequent embezzlement case, and according to the film's epilogue, resulted in all Nevada casinos being required by law to post the toll-free number for the Nevada Council on Problem Gambling , should any of their clientele need it.
The film is told via a series of flashbacks, including voice-over narration, in which Laura Bancroft (Burke) is giving her testimony before Gamblers Anonymous, detailing how her gambling addiction ruined her life.
As the story begins, Laura is married to her second husband Jim (McRaney), and the mother of two children, Jennifer (Ellen Page) and Tommy (Matthew Harbour). The family has just moved from Florida to Reno, Nevada, where Laura has landed a job as head of fundraising for the Children's Chronic Illness Association.
Out on the town one evening, Laura decides to give a video poker machine a try. She makes the acquaintance of Bella (Joyce Gordon), a sweet older lady and casino semi-regular, on whose advice Laura steps "upward" to slot machines, where she experiences a bit of beginner's luck. Not long after, while grocery shopping with Jennifer and Tommy, they see slot machines in the store, and though Laura initially claims playing them is "just throwing money away," the kids encourage her to try, and she ends up winning another small jackpot.
Gradually becoming addicted to gambling, things start to take an ominous turn when Laura begins smoking again. She then misses a special luncheon at Jennifer's school after stopping by the casino and losing track of time, though Laura lies and claims she was stuck in a conference at work. Tommy then accompanies her for a night of gambling, despite it being a school night and his having an important test the next day. While the two are out, Laura fails to answer her cell phone when Jennifer, whom she was supposed to pick up from the local recreation center, tries to call her. This forces Jennifer to accept a ride from two questionable older boys. Angered over Laura's sudden negligence, Jim attempts to discuss the problem with Laura, but she blows him off. Desperate to get out of the financial hole caused by her insatiable gambling habit, Laura is able to get her mother to loan her $10,000, but quickly loses this as well.
Having found unpaid bills, Jim goes down to the casino and confronts Laura about her growing addiction, but she again denies having a problem and promises to take care of the bills, though she chooses to do so by embezzling from her organization (which no one initially suspects, due to Laura's job skills). She also begins neglecting her kids, even pawning both their personal possessions and Jim's. As a result, Jennifer is forced take over cooking and cleaning for the house, as well as checking Tommy's homework. Additionally, Jennifer begins rebelling, causing her own school attendance and performance to decline sharply, as well as picking up her mother's smoking habit.
Things suddenly turn around for Laura when, during one of her frequent casino excursions, she wins $50,000 by managing a very rare royal flush on a video poker machine, for which she also receives a complimentary stay in a suite from the casino. Informing Jim (who's now working double shifts as a mechanic to keep his family going) about her good fortune, he angrily confronts her with various pawn receipts, and tells her they need to use that money to pay bills and retrieve their personal possessions. However, Laura continues to deny the reality of her addiction, instead blaming Jim for not making enough money, then accuses him of wanting out of the relationship, ordering him to vacate the house.
While Jim packs his bags and shares a tearful goodbye with Jennifer and Tommy, Laura foolishly gambles away her winnings, managing to lose every penny of it in less than an hour. Now left to fend for herself, Laura manages to scrape together enough money for a grocery shopping excursion, but gets distracted by the slot machines in the local supermarket and is left afterwards with only enough for a box of oatmeal. Feeling completely helpless, Laura seriously considers suicide, but decides against it for fear of not wanting to orphan her children. Jennifer later calls Jim, begging him to take her and Tommy; unable to do so, but not wanting them to continue living as they are, he brings the kids to Laura's mother's house. After another day at the casino, Laura attempts to retrieve her kids, but Lois refuses to hand them over, insisting that they remain there until her daughter gets her life together.
Laura tries to take out a loan on her home, but only qualifies for a small amount. She then attempts to borrow from Bella, who protests that they don't have that kind of friendship, and that she can't help her. Laura then angrily blames Bella for causing the problem by introducing her to the slots, but Bella points out that she didn't cause Laura's addiction and reminds her "there's only one way to double your money in Reno: fold it in half, then put it back in your purse."
Her addiction now completely out of control, Laura embezzles a total of $100,000 from her charity. Having lost everything (including her house, to foreclosure, as well as her kids), she finally is caught when an auditor from the organization's Maine chapter comes by Laura's office to conduct a random audit, and discovers her dishonesty. In the meantime, Jennifer has gone missing after sneaking out the previous night to attend a rave, and Lois shows up at Laura's house to inform her about the situation. Overwhelmed by her rapidly collapsing world and unable to focus on anything else, Laura attempts to blame her mother for setting unrealistically high standards that she couldn't live up to, but Lois immediately shuts her down. She then tells her daughter that she'll find Jennifer, but will continue to maintain custody of the kids until Laura gets her addiction under control. Finally admitting she has a serious gambling problem, Laura shares a tearful embrace with her mother.
When Jennifer returns a short time later, Lois tells her that staying out all night is unacceptable, and though she initially tries to blow her grandmother off, Lois informs Jennifer that Laura's problem doesn't have to be hers, and that she and Tommy are good kids who deserve a chance. She then asks if Jennifer misses having someone to care about her, and assures her that she cares for both of them.
In the end, Laura finally decides to fully own up to her misdeeds, explaining the situation in detail to her kids before doing so, but is found guilty in court and sentenced to fifteen months in prison, three years of supervised release and paying restitution. The final scene shows Laura bidding a tearful farewell to her children before being led away to serve her prison sentence.