As the story unfolds, Felix Keene (Bill Murray) shares a crucial piece of advice with his daughter Laura (Rashida Jones), warning her to be cautious about giving her heart away. Ironically, Laura soon finds herself married to the charismatic Dean (Marlon Wayans). Settling into a seemingly idyllic life with their two young children, the couple appears happy. However, beneath this façade, tensions quietly fester. One evening, after returning from a business trip, Dean's advances toward Laura are met with a disconcerting silence, leaving her feeling isolated and anxious.
Laura's unease intensifies as she grapples with her struggles to write her new book, which she feels pressure to complete. Seeking counsel, she reaches out to Felix, who is enjoying a vacation in Paris. During their phone call, Felix offers cryptic advice: he suggests she "think like a man." This unsettling suggestion leads Laura to suspect that Dean may not be the faithful partner he seems.
Complicating matters, Laura stumbles upon a mysterious purse with body oil hidden in Dean's luggage, igniting her suspicions. At a work function for Dean, she feels increasingly out of place among his colleagues—especially the alluring Fiona (Jessica Henwick), whose flirtations with Dean only heighten Laura's concern.
Confronting Dean about the purse reveals a dismissive attitude, acting as a wake-up call for Laura to reevaluate their relationship. Lunch with Felix allows her to vent her frustrations, and he shares tales of his own infidelities, warning her about men and their deception. Amusement and disbelief intertwine as Laura watches her father flirt with every woman he encounters, yet his probing nature starts to cast doubt on her perceptions of Dean.
As her birthday approaches, Laura discovers that Dean has plans that don’t include her. Felix, outraged, encourages her to investigate Dean’s phone. Though Laura feels pressed for time, her growing suspicions further entwine with her doubts about Dean's fidelity.
Felix dedicates quality time with his granddaughters, but Laura's patience starts to wane as his outdated outlook annoys her. Dean’s absence on her birthday exacerbates her feelings of neglect when he surprise FaceTimes, gifting her a kitchen appliance that hardly excites her. Regardless of her insistence that she doesn't want to celebrate, Felix insists on taking her out, leading her eventually to join him after some coaxing. When he inquires about jewelry, Laura's disinterest prompts Felix to reveal he has been watching Dean, indicating that he had even surveilled him at Cartier.
During dinner together, Felix surprises Laura with a coveted watch, suggesting it’s time to uncover the truth about Dean. Initially hesitant, Laura ultimately agrees to follow Dean to find out what might really be happening behind the scenes. After another awkward dinner where she feels discarded, Dean leaves for another "work engagement," presenting an open invitation for Felix and Laura to investigate Dean's movements.
With Felix's guidance, they sneak around in his sleek red convertible, ultimately spying on Dean and Fiona entering a restaurant. While they partake in a little midnight snack prepared by Felix, Dean calls Laura claiming he has a late-night work dinner. This only increases her unease. The undercover operation escalates when Dean and Fiona leave together, prompting Felix to chase after them in pursuit, creating a thrilling chase interrupted by a police officer whom Felix charms into letting them go.
Tension builds as Felix shows Laura incriminating photographs of Dean and hints at a spontaneous trip to Mexico that Dean might have planned. Initially skeptical, Laura is stunned when she finds out Dean indeed has a last-minute trip. With Felix persuading her to join him on this surprise getaway, they face mixed feelings about leaving her children behind with their grandmother.
Upon their arrival at the resort, Laura is surprised to see Felix serenading the crowd, suggesting that this destination is one of his old haunts. Yet, their vacation takes a serious turn as Laura confronts Felix about the past mistakes that ripped their family apart. Felix's honest revelation touches on his emotional fulfillment and how that led to infidelity, adding layers to Laura's struggle with her own relationship.
Things heat up as Laura and Felix attempt to gather information on Dean, only to find unexpected guests in their shared space. Their plans unravel further when Dean unexpectedly contacts Laura about his early return home, leading to an encounter with Fiona that leaves her in shock.
Feeling betrayed, Laura lashes out at Felix, accusing him of sabotaging her marriage while being self-absorbed. Struggling to reconnect with Dean, they begin to address the emptiness and misunderstandings that have pushed them apart.
With their relationship explored and vulnerabilities shared, Laura finds solace in her writing, slowly rebuilding her emotional equilibrium. Felix, eager to mend their relationship, suggests another spontaneous trip, but Laura, in a moment of growth, politely turns him down, appreciating the sentiment instead. Their bond rekindles as Laura and Dean finally celebrate her birthday under brighter circumstances, marked by thoughtful intentions that rekindle the warmth between them. Dean's gift— a Cartier watch— symbolizes a new beginning, making Laura's birthday a moment filled with promise and hope.
