When Joel, portrayed by Paul Rudd, first crosses paths with Molly, played by Amy Poehler, it’s a clash of opposites: their initial encounter is marked by mutual disdain, as his large corporation, CSR (Candy Research and Systems), poses a serious threat to her charming indie candy shop. Struggling with her recent breakup, Molly's clumsy demeanor adds to the tension, while Joel is entangled in a complicated relationship with the alluring Tiffany Amber Thigpen, played by Cobie Smulders, who seems to care little for him. Joel's workplace is rife with competition, particularly from his rival Trevor, portrayed by Michael Ian Black, who seeks to undermine him at every turn, and his boss, Roland, played by Christopher Meloni, is equally unforgiving.
As fate would have it, Molly discovers CSR's plans to erect a massive store right across from her shop, which leads her to visit her accountant, Eggbert Flaps (Ed Helms), who delivers the grim news that her business is doomed within six months. Meanwhile, a heartbroken Joel is taken aback when he unexpectedly catches Tiffany in an intimate moment with Trevor, prompting her abrupt departure from his life. Seeking solace, Joel invites his brother, Jake (Max Greenfield), a carefree slacker, to stay with him for a few days.
The plot thickens when Joel and Molly are thrown together at a Halloween party, where they're clad in identical costumes, leading to a comedic confrontation. Their mutual friends, Bob and Brenda, step in to facilitate an introduction. Molly is initially irked to learn that Joel is affiliated with CSR, yet she can’t deny his charm. A chance encounter at a local used bookstore ignites something between them as they discover shared interests. Molly, reflecting on her first impression of Joel, reaches out for a casual coffee date that blossoms into a deeper connection, leading her to invite him over for dinner where they share personal dreams.
Their romance takes a turn when Joel learns about Molly having a son, making things more complicated as he struggles with their relationship due to his lingering feelings for Tiffany. After an awkward dinner, where an incident reveals Molly's parents' unsettling beliefs, Joel confronts Molly, leading to a heated argument that ends with him storming out. In a moment of weakness, he finds solace with Tiffany once more, only to realize this wasn't meant to be.
As Thanksgiving approaches, tensions rise at a gathering hosted by Bob and Brenda, showcasing the love-triangle complexities involving Molly, Eggbert, Joel, and Tiffany. Fast forward to New Year’s Eve, Eggbert proposes to Molly, who accepts, but Joel starts to connect the dots about Tiffany's true intentions. After a heart-to-heart with his grandmother, he recognizes that Molly is the one he truly wants.
In a bold move, he requests his boss Roland to spare Molly's shop, a plea that results in a big promotion for Joel—a promotion he ultimately declines, choosing instead to pursue his passion for opening a coffee shop named "A Cup of Joel." In a dramatic turn of events, Joel rushes to stop Molly's wedding, only to discover she's just left Eggbert at the altar, realizing he wasn’t her soulmate.
Their love rekindles, and they marry in the same spot a year later. However, life takes unforeseen turns; Molly's shop ultimately fails as CSR expands its dominance, and despite Joel’s dream of "A Cup of Joel," it doesn't quite take off. This leads to conflict within their new family dynamics as Molly's son begins to resent Joel, culminating in the heart-wrenching decision for them to file for divorce while still maintaining a friendship.
