Thaddeus "Thad" Baxter, an event coordinator in New York City, opens the story by addressing the reader directly. His fiancée, Naomi, is pregnant, and he can no longer afford both a wedding and a home. He discovers that
The Wedding Game, a DIY wedding reality show on the DIY Network, is casting couples; the show covers the wedding, and the grand prize is a Manhattan penthouse. One rule requires each team to include a family member, so Thad turns to his older brother, Alec Baxter, a top divorce attorney who protected him during their parents' constant fighting by sneaking him out to a bakery for cannoli. The brothers have since drifted apart, barely speaking every few months.
Meanwhile, Luna Rossi, a 30-year-old crafting entrepreneur with a top-ranked Etsy shop and a Webby-winning YouTube channel, spots the same casting call. Luna has been her older brother Cohen's protector since he came out as a teenager, following him from Connecticut to New York. She envisions Cohen, a carpenter, and his fiancé, Declan, a Chinese American public school teacher, as ideal contestants; they had planned a courthouse wedding despite Cohen's private wish for a real celebration. Cohen refuses when Luna pitches the idea, so Luna fills out the application behind his back on a suggestion from her roommate and best friend, Farrah. When the couple is selected and Luna confesses, Cohen is furious but agrees after Declan supports the idea.
Alec, whose cynicism about marriage stems from watching his workaholic father and emotionally absent mother destroy each other, initially refuses Thad's request. Thad reveals Naomi's pregnancy and accuses Alec of becoming their absent father. Alec's friend and colleague, Lucas, who lost his own brother to alcohol poisoning during a fraternity pledge, urges Alec not to waste the time he has. Alec relents.
Filming introduces three teams: Team Rossi (Cohen, Declan, Luna), Team Baxter (Thad, Naomi, Alec), and Team Hernandez (Luciana and Amanda, the engaged couple, along with Amanda's overbearing mother, Helen). Alec mistakes Luna for a production assistant and demands coffee; she spits in it before delivering it. When Thad pushes Alec to apologize, Alec picks a fight instead. In the first challenge, Team Baxter wins with a chaotic "Flamingo Dancer" vision board, while Luna's polished "Modern Rustic" board places last.
Over the following weeks, Team Rossi dominates under Luna's leadership, winning challenges for venues and invitations while Team Baxter flounders. After a disastrous bouquet challenge in Week Five, Thad breaks down crying, and Naomi confronts Alec, telling him she is unimpressed with the man Thad idolizes. She reveals that the first dream Thad wrote in a notebook Alec gave him at graduation was to be a protector like his brother.
Alec decides to take the competition seriously. He creates a fake Instagram account called "ChrisEcrafts" to message Luna for her cake recipe, and Luna shares it freely, charmed by the friendly exchange. The next day, Alec disguises himself in a fedora and sunglasses and follows Luna to a baking supply store, copying her purchases. He crashes into a macadamia nut display and knocks bottles from a shelf before Luna tears off his disguise. Dropping his pretenses, Alec confesses that his relationship with Thad is "practically extinct" and he does not want to fail his brother again. Moved by his vulnerability, Luna offers him baking advice.
Their antagonism thaws into friendship, then into something deeper when Luna comes to Alec's apartment for tacos and a baking lesson. Over two evenings, she teaches him to bake a proper cake while he opens up about a childhood devoid of parental warmth. They produce a two-tiered naked cake with berries, and their connection deepens. On cake challenge day, Alec adds almond extract to his frosting, and his three-tiered creation wins first place for Team Baxter for the first time. That evening, Luna visits his apartment, and the night ends with their first kiss. Alec asks to keep their relationship secret until after the show, fearing Thad would see it as betrayal, and Luna reluctantly agrees.
They date secretly, growing closer. Alec calls his estranged mother for the first time in years and invites her to the next taping, but she does not show, citing a "rough night," an excuse rooted in her dependence on prescription medication. Luna finds Alec drunk and tearful at his apartment that night. He breaks down, asking why his mother does not love him, and Luna stays, holding him as they fall asleep. The next day, judge Marco Vitally offers Luna a collaboration on a line of wedding invitations, a milestone she keeps from Alec because of his fragile state. Both acknowledge they are falling in love.
Everything collapses during the final challenge. Alec tosses Luna a burlap ribbon she had mentioned to him in private, revealing their closeness. Mary DIY, the show's host, having spotted them holding hands at a restaurant, publicly announces their relationship on set. Thad erupts, accusing Luna of sabotage and telling Alec they are "done." Cohen unleashes years of frustration, accusing Luna of controlling his life, from how he came out to their parents to every decision in the competition, and walks off set without her. That evening, Luna and Alec fight. She blames him for making her lie and tells him she "chose wrong" by choosing him. Alec quietly replies that he thought he chose correctly because he chose her, and leaves.
Both are devastated. Alec begins therapy, visits his mother to retrieve childhood photos, and creates a scrapbook for Thad divided into past, present, and empty future pages. Thad is moved but not yet ready to forgive. Naomi gives Alec the baby's ultrasound photo and asks if he loves Luna; he admits he does. Alec visits Cohen and Declan, takes full responsibility for the secret, and tells Cohen he is in love with Luna. Cohen reconciles with Luna the night before his wedding, apologizing and acknowledging she has always been a loving sister.
Three weddings take place over one weekend. At Cohen and Declan's Friday ceremony, Cohen delivers emotional vows about learning to love openly; Luna and Alec exchange painfully stilted small talk, and Alec leaves early. On Sunday morning before Thad's wedding, the brothers fully reconcile in the groom's suite when Alec presents Thad with their grandfather's cuff links—a sentimental heirloom Alec had worn at his own college graduation—to wear at the ceremony, with Thad admitting the scrapbook made him sob. At the reception, Cohen nudges Luna to ask Alec to dance. She crosses the floor and extends her hand. Alec takes it, pulls her close, presses his forehead to hers, and tells her he loves her. Luna says she loves him back and apologizes for saying she chose wrong. They kiss on the dance floor as their families cheer.
In an epilogue set weeks later, Team Hernandez wins
The Wedding Game by America's vote. Luna is moving into Alec's apartment, where he has converted a bedroom into a craft room for her. Her career thrives with the Marco Vitally collaboration and a column in
Brides magazine. Thad and Naomi, expecting a girl, will take over Luna's vacated rent-controlled apartment. Every Sunday, the extended family gathers for brunch, and Alec, who now calls Luna's parents Mom and Dad, reflects that the love he never thought he wanted was exactly what he needed.