The Devil Wears Black

Maddie Goldbloom, a 26-year-old wedding dress designer at Croquis, a bridal company partnered with Manhattan's Black & Co. department store, returns from a date with Ethan Goodman, a pediatrician she has been casually seeing, and finds her ex-boyfriend, Chase Black, waiting on her stairway. Chase, the 32-year-old chief operating officer of Black & Co. and the son of its founder, Ronan Black, is cold, sarcastic, and always dressed in black. Maddie, nicknamed "Martyr Maddie" for her inability to say no, broke up with Chase six months earlier after catching him with another woman at his apartment.

Chase reveals that his father has been diagnosed with incurable stage-four prostate cancer and has roughly three months to live. He never told his family about the breakup and, after the diagnosis, impulsively told them he and Maddie were engaged, hoping to give his distraught family something positive to focus on. His mother, Lori, has a history of depression, and his sister, Katie, a marketing executive at Black & Co., has severe anxiety. A fake engagement party is planned in the Hamptons that weekend. Maddie initially refuses, but Chase leverages threats and emotional appeals, reminding her of losing her mother, Iris, a florist who died of breast cancer when Maddie was 16. Each of Maddie's chapters opens with a letter Iris wrote during her illness. Maddie agrees to attend the one weekend, stipulating the arrangement must remain secret at work, and Chase gives her an engagement ring.

Chase's narration reveals his side of their relationship. He intended Maddie to be a fling, but they settled into a comfortable routine. He gave her a key to his apartment and brought her to meet his family at Christmas without recognizing these as signs of commitment. When Maddie pointed out he was her boyfriend, Chase panicked and deliberately brought a woman home to provoke a breakup, hoping she would eventually return as a casual hookup. She never came back.

At the Hamptons estate, Maddie meets Julian Black, Chase's older cousin raised as his brother after Julian's parents died in a car crash, and Julian's wife, Amber. Julian, the chief information officer at Black & Co., resents Chase for being named Ronan's successor as future chief executive officer (CEO). That night, Maddie overhears Julian accusing Chase of faking the engagement to secure the CEO position and dismissing Maddie as "a six." Despite this, Maddie bonds with the family, and she and Chase begin exchanging handwritten notes. Julian corners them into extending the charade by inviting everyone to a Friday dinner at his apartment.

At the dinner, Ronan collapses. Chase calls his best friend, Grant Gerwig, a prestigious oncologist, who stabilizes Ronan over the phone. Afterward, Maddie and Chase share a vulnerable moment on her stairway, pressing their foreheads together as she speaks about grief from personal experience. Chase later reveals the truth about his supposed cheating: He never slept with the woman and brought her home deliberately because the relationship was becoming too real. Years earlier, his fiancée, Amber, left him for Julian when Chase could not guarantee he would become CEO. Amber quickly became engaged to Julian and was already pregnant with their daughter, Clementine, by the time Chase returned from abroad. The experience destroyed Chase's belief in romantic love.

Chase proposes a test of commitment: identical azalea plants, notoriously difficult to keep alive, for himself and Ethan. Despite this gesture, Maddie tells Chase she cannot be his "fake-real girlfriend" because she fears developing feelings again. Meanwhile, her boss, Sven, assigns her to design the Dream Wedding Dress (DWD), the flagship gown for Croquis's runway show at New York Fashion Week. She creates an unconventional crème-colored gown she names the Moonflower, after a flower that blooms in darkness, and refuses to simplify it when Sven expresses reservations.

When Ronan is hospitalized after a heart attack, Maddie rushes Chase to the hospital and takes charge. The next morning, Katie catches Julian trying to slip a contract in front of the still-recovering Ronan that would name Julian emergency CEO. Chase punches Julian and destroys the documents. Chase asks Maddie to a family weekend at Lake George, and she agrees. Julian invites Ethan as a guest, hoping to expose the fake engagement. After a tense dinner, Maddie ends things with Ethan. At dawn, Chase kisses her, and they sleep together for the first time since their breakup. Maddie accepts but sets ground rules: no more than three sleepovers per week, and when it ends, Chase must let her go permanently.

They quickly exceed every rule. At work, Nina, a coworker who has bullied Maddie, catches them together and leaves a mocking note. Chase alerts Sven to the bullying, resulting in Nina's firing, but Maddie convinces Sven to rehire her, offering Nina a second chance. The fake engagement unravels when Julian presents Chase with a paternity test proving Julian is not Clementine's biological father and accuses Chase of being her real father. Chase attacks Julian in his office, and Ronan arrives to overhear everything. Maddie flees and ends the arrangement. Chase takes his own paternity test, confirming he is not Clementine's father. He goes to Maddie's apartment in the rain to explain, but she asks him to leave. For the first time, he respects her boundary. Standing in the rain, he realizes he is in love with her.

Maddie visits her mother's grave and speaks aloud about her growth, acknowledging she has stopped being afraid to disappoint people. She and Chase begin spending time together platonically. When Ronan dies, Maddie comforts the family and takes Chase home, where she discovers the azalea plants in full bloom in his pantry, which he converted into a humid growing space. She does not tell him what she found. Ronan's will contains personal messages for each family member. His message to Chase states that if Chase is sitting there without Maddie, he has failed. Ronan also leaves Maddie his mother's vintage sewing machine, with a note about how his seamstress mother inspired the founding of Black & Co.

At New York Fashion Week, the model hired to walk in the Moonflower falls ill. Because the dress was made to Maddie's measurements, Sven, Nina, and Maddie's best friend and next-door neighbor, Layla, convince her to model it herself. Sven then leads her to a room where Chase is waiting with their families and friends. Chase tells Maddie he drove to Pennsylvania to meet her father, that he called her "Mad" because he was mad about her, and asks her to marry him. Maddie says yes. Chase carries her onto the runway, introducing her to the audience as his favorite bridal creation.

In the epilogue, set six months later, they marry in her father's backyard. A letter Ronan wrote before his death reveals he knew the engagement was fake but recognized Maddie as the one from the way Chase looked at her. At the altar, Maddie texts Chase a message she immediately deletes. He demands to know what it said, and she tells him she is pregnant. Eight months later, their son, named Ronan, is born. Maddie reflects on her mother's final letter, which advised her to marry a man she could laugh with, and on the letters she has begun writing to her own son.