Jessie Barnes, the owner of a hair salon called Honeysuckle Salon, is in her third trimester of an unexpected pregnancy and tangled in a lie she told her grandfather, the man who raised her after her mother died and her father abandoned the family. When her boyfriend, Jonathan, left her upon learning she was pregnant, Jessie panicked and told her grandfather she was engaged, then maintained the fiction of a fiancé who was always conveniently unavailable. Jessie's best friend, Lucy, persuades her brother, Drew Marshall, an ob-gyn, to pose as Jessie's fiancé for a visit from her grandfather, but Drew never shows up. The scheme turns out to be unnecessary: Her grandfather's car trouble delays his visit, and he admits he has known all along there was no fiancé. Still, Jessie is furious at Drew on principle, and that night a pipe bursts under her sink, flooding her home.
Drew's absence has a simple explanation. He had been awake for over thirty hours delivering babies at the hospital and had collapsed into sleep without setting an alarm. His exhaustion also leads him to make an impulsive mistake: When a colleague, Dr. Susan Landry, hints at asking him out, Drew blurts that he already has a girlfriend, naming his sister's best friend. He wakes hours later to fifteen missed calls from Jessie and a scathing text message, which kills any impulse to apologize.
The burst pipe reveals black mold and rotting infrastructure beneath Jessie's house, requiring weeks of construction. She moves in with Lucy and Lucy's husband, Cooper, who is also Drew's best friend. The arrangement proves miserable: Lucy's young son wakes Jessie at five every morning, the hot water runs out mid-shower, and she has no privacy. Lucy suggests Jessie stay at Drew's spacious house instead, but Jessie flatly refuses.
Meanwhile, Drew needs a fake girlfriend for the medical fundraiser gala where Susan expects to meet his nonexistent partner. Lucy engineers a trade: Jessie will pose as Drew's girlfriend for one night, and Drew will let her stay rent-free at his house. Despite their mutual hostility, both recognize the practical value of the deal. Jessie agrees but secretly begins plotting revenge, planning to humiliate Drew at the gala as payback for standing her up.
On moving day, Jessie deliberately packs her entire house, knowing that cluttering Drew's minimalist home with colorful throw blankets, Christmas mugs, and decorative pillows will drive him crazy. They battle over the volume of belongings, and overnight Jessie unpacks everything throughout the shared living spaces. Drew retaliates by hiring movers to repack her boxes and stack them in her bedroom so densely she cannot reach her bed.
Their prank war escalates. Drew hides Jessie's underwear after she sneaks her laundry into his wash; she steals the Frosty mug he placed on a trophy shelf above his bedroom door. Jessie and Lucy stage an elaborate hoax involving Lucy posing as a "birth guru" in matching red robes. Drew plays along, pretending to be fooled, until Jessie reveals the real prank: a bucket of water rigged above his bedroom door, which drenches him. Drew laughs genuinely, and Jessie is alarmed to realize she can no longer dismiss him. When Drew attempts his own prank by hiding in her closet, she opens the door wearing only a towel and punches him in the face out of fright, giving him a black eye.
Beneath the pranks, a quieter shift takes place. When Drew has a severe migraine, Jessie tends to him, closing curtains, bringing ice, and massaging his neck. She is startled by how much she cares. They begin sharing meals, watching TV, and doing laundry side by side. Drew leaves blankets over Jessie when she falls asleep on the couch during her insomnia-plagued nights. A silent breakfast becomes a turning point: They eat without speaking, and when Jessie's arm brushes Drew's at the sink, they share a long, loaded look that neither can categorize.
At the gala, Drew arrives late and spots Jessie across the ballroom in a black dress. He tells her she is beautiful, and they nearly kiss before Susan interrupts. During dinner, Jessie executes her revenge: She drops a ring box, and when Drew picks it up from a kneeling position, she loudly accepts his "proposal" in front of five hundred colleagues, trapping him in a fake engagement with a comically tiny ring. Drew retaliates by kissing her deeply in front of the entire room, leaving both of them shaken. Afterward, through her locked bedroom door, Drew confesses he has been flirting with her and asks if something real exists between them. Jessie lies, saying she is not attracted to him, because she is terrified of being hurt again. Drew accepts the rejection and calls Mia, a woman who had given him her number at a coffee shop, to ask her on a date, which Jessie overhears. They negotiate a final deal: Drew had accepted an invitation during the gala to spend a weekend at the lake house of Dr. Richard Green, a former mentor from medical school, and Richard's husband, Henry, and still needs Jessie to accompany him as his partner. In return, Drew will drive her to visit her grandfather in Kentucky.
Jessie drags Lucy on a stakeout outside the restaurant where Drew takes Mia and is flooded with jealousy when she sees them together. Drew spots her, and later neither fully admits what is happening between them.
On the drive to the lake house, they hold hands the entire way. Jessie's contractor calls with bad news: The repairs will extend until her due date. She breaks down, confessing she has avoided preparing for motherhood altogether. Drew tells her firmly that she and her baby will never be homeless and that his house is hers as long as she needs it. At the lake house, Drew declares he is done avoiding his feelings and kisses Jessie on the porch. She does not stop him but refuses to acknowledge her feelings verbally. That night, sharing a bed, Drew gives her a prenatal massage, and they shop online for baby items together. He tells her she has taught him how to rest and let go of his constant need to be in control.
The next morning, a pillow fight becomes the vehicle for Jessie's emotional breakthrough. She confesses she is terrified Drew will leave her and the baby the way her father and Jonathan did. Drew tells her he wants her deeply, and Jessie whispers that she wants him too and asks him to be good to her. He promises he will. On the drive to her grandfather's house, she writes "Jessie + Drew" on his Jeep's glove box and tells him everything: Jonathan's cruelty, her father's abandonment, and that she hated Drew on purpose from the moment she saw his photo, because she recognized he was exactly the kind of man she could fall for. At her grandfather's house, the old man subjects Drew to a polygraph test and asks if he loves Jessie. Drew says yes and receives his blessing.
They return home to a surprise baby shower organized by Lucy and Cooper, funded by Drew's credit card. Drew leads Jessie upstairs to reveal a fully furnished nursery he arranged so she will have a place to bring the baby home to regardless of her house's timeline. Jessie tells Drew she loves him, and he says it back. When her contractor later calls to say her house is unexpectedly ready, they agree through a playful, coded conversation that Jessie will stay permanently.
Drew reluctantly leaves for a one-night camping trip, and that evening Jessie goes into labor at Lucy's house. She cannot reach Drew because his phone has no service. Lucy rushes her to the hospital, where she labors for twelve hours. Drew finally sees the messages at five in the morning, calls from the road, and coaches Jessie through the final stages by phone. He arrives minutes after she delivers and cries when she tells him it is a girl. She names the baby Jane Alexandria Barnes.
Eight weeks later, Drew proposes with a real ring, and Jessie says yes. Her grandfather sells his Kentucky home, buys Jessie's Nashville house, and moves nearby. In a bonus epilogue set roughly three years later, Drew and Jessie are married with two children, Jane and baby Graham. Lucy reveals she had been subtly engineering Drew and Jessie's relationship from the start, making Jessie uncomfortable at her house so she would move to Drew's and throwing them together at every opportunity. Both Drew and Jessie are stunned to learn they, the self-proclaimed king and queen of schemes, had been outmaneuvered all along.