NOTE: This spoiler was written by Mary. who says, "The story lines mix together so much that it's hard to keep it chronological, so I'm breaking them apart just to tell them separately, and less confusingly."
Reed (Ashton Kutcher) proposes to his girlfriend Morley (Jessica Alba) on the morning of Valentine's Day, which she accepts. Everyone he tells this to is shocked, including his friend Alphonso (George Lopez) and best friend Julia (Jennifer Garner). Reed and Alphonso work at a florist, where many of the characters in the movie come to buy flowers for Valentine's Day. One of these people is Dr. Copeland (Patrick Dempsey), Julia's new boyfriend. When he is ordering flowers from Reed, who he hasn't formally met yet, Reed discovers Dr. Copeland is ordering two different arrangements - one for Julia, and one for his wife Pamela.
Morley comes into the shop not wearing her engagement ring, since she says she isn't ready for people to be all giddy over it. When Reed comes home to leave her a surprise bouquet, he discovers her packing her things. She gives him the ring back and they break up for good. Reed then runs to the airport to stop Julia from flying to San Francisco to surprise Dr. Copeland; he tells her he is married, but she won't believe him until she goes to the hospital where he works and finds out for sure. She then goes to the restaurant where Dr. Copeland is having dinner with his wife, and makes Pamela realize that her husband has been having an affair. Julia goes to her friend Kara's (Jessica Biel) I Hate Valentine's Day party, where her elementary school student Edison confesses his love to her. Julia tells Edison that another student has a crush on him, and he gives his flowers to her instead. This makes Julia realize she is actually in love with her best friend, and she finds Reed and they kiss.
Kara is a publicist for Sean Jackson (Eric Dane), a famous football player that has been released from his team. While discussing his future with Kara and his agent Paula (Queen Latifah), he realizes what he actually wants to do. He calls a press conference and tells everyone that he is gay, but will continue to play football. At the press conference is sports reporter Kelvin (Jamie Foxx), who has been reporting Valentine's Day fluff all day at the request of his boss, Susan (Kathy Bates). Kara complains to him that she is alone on Valentine's Day, and invites him to her I Hate Valentine's Day party. He shows up and tells everyone that he is her date, and later when she visits him at the TV station, they kiss.
Paula's assistant, Liz (Anne Hathaway) has just had a one-night stand with a worker in the mailroom, Jason (Topher Grace). Jason just moved to Los Angeles from Indiana, and is concerned when she rushes out the next morning. When he discovers it is Valentine's Day, he thinks she is mad that he didn't acknowledge that in the morning, but she actually ran off because she had to do her other job, which is a phone sex operator. Jason asks her out for that night, which she accepts. However, when she is at dinner, she gets a phone call from one of her clients, and runs outside to take it. Jason finds her outside and finds out what she does, saying he can't handle it. When she asks if he'll call her, he says "I would, but I don't think I can afford it." Insulted, she runs off. Later that night, he goes to an outdoor movie screening at a Hollywood cemetery, where he meets Edgar (Hector Elizondo), who has just discovered his wife Estelle (Shirley MacLaine) had an affair about thirty years ago. Estelle comes to the cemetery to apologize, and they make up to an applauding audience. This inspires Jason to go apologize to Liz, who eventually accepts.
Edgar and Estelle's grandson is Edison, who is in love with his teacher Julia. They are upset that Edison is having such a disappointing Valentine's Day, since he used to make handmade cards with his mother, who is not there. Edison's babysitter is Grace (Emma Roberts) who is planning on having sex with her boyfriend Alex (Carter Jenkins) for the first time that day. He goes to her house to set up, but Grace's mom comes home early and catches him there. Afterwards, they decide to wait, even though they will be going to college on other sides of the country. Their best friends are Willy (Taylor Lautner) and Felicia (Taylor Swift), who are your typical PDA high school couple, sending each other huge gifts and making out everywhere.
The best storyline of the movie is between Holden (Bradley Cooper) and Kate (Julia Roberts) who meet on a plane headed for Los Angeles. Holden is a businessman coming back from a trip, and Kate is an army Captain who gets to come home just for Valentine's Day. They hit it off pretty quickly, though Kate doesn't want to give up any details about who she is visiting for just one day. Kate comments that the flight attendant on the plane keeps looking at him, but he is clearly not interested. He says he just got out of a relationship, and hates the idea of Valentine's Day. When the disembark, Kate is unable to get a taxi or a car, and is in a hurry. Holden gives her his private car, and she thanks him profusely before driving home to her Valentine - Edison, her son who she hasn't seen in a year. Holden goes home and finds his Valentine - Sean, who he is proud of for finally coming out publicly.
And, Morley and Dr. Copeland end up alone.
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