Michael Ryan (C. Thomas Howell) is a high school student who receives a passionate anonymous love letter. Michael is obsessed with the class beauty Deborah Anne Fimple (Kelly Preston), and his best friend Roger Despard (Casey Siemaszko) convinces him that the letter is from her. However, he is totally oblivious that his close friend Toni Williams (Lori Loughlin) is in love with him. Michael writes Deborah a passionate anonymous love letter in return, and asks Toni to give it to her. Toni reads the love letter and, realizing it's poorly written and unromantic (since Michael has copied words from greeting cards), she rewrites it.Deborah's mother, Elizabeth Fimple (Leigh Taylor-Young), discovers the letter. Her jealous police officer husband, Lt. Lou Fimple (Fred Ward), sees her reading it. He steals the letter, and believes that his wife is having an affair. He suspects his neighbor (and bridge partner) George Ryan (Cliff De Young). George also reads the letter (although by mistake) because Lou's wife is his night school teacher and it somehow ends up in his book. When George asks he about it, he assumes she wants to have an affair with him, despite the fact that she is friends with his wife. Meanwhile, Lou shows the letter to George's wife, Connie Ryan (Dee Wallace), and proposes that they expose the adulterers. Receiving no response from Deborah, Michael writes a second love letter, which Toni again rewrites.Michael experiences a series of wacky adventures with his friends through the summer before his senior year of high school. After Toni arranges a meeting between the two, she tells Deborah that he wrote the love letters, and she finally agrees to a real date, during which they are almost caught by Deborah's jock college quasi boyfriend Steve Powers (Scott McGinnis), but Toni intervenes by pretending to seduce him and later ditches him. After a short while, Michael realizes Deborah is snobbish and shallow - not like he expected her to be - and begins to realize his true feelings for Toni. Eventually, Michael and Deborah break up at his birthday party, refuses to sleep with her when she intends for this to be his birthday present. Eventually, Lou and Connie cannot control themselves at a bridge party: Lou assaults George, and Connie has a breakdown in front of her friends.When Michael returns home, he finds his parents arguing and his mother reading his letter; Michael angrily tells his parents the letter actually belongs to him while scolding them for invading his private mail, leaving them in a state of shock. At Deborah's house, Lou confronts Elizabeth about the letter; Deborah overhears him reading the words and tearfully reprimands him, revealing the letter is hers, which leaves Lou in a state of shock. Angered that her parents invaded her privacy, Deborah heads to her room and breaks down into tears. Michael later returns to Toni's house, confessing that nothing happened between him and Deborah, and in the process, confessed his feelings for Toni and wonders if anything can ever happen between them. However, refusing to admit her feelings after everything that happened, Toni rejects Michael.Just as the fall semester is about to begin, Deborah confronts Michael about the letters, but upon seeing them, Michael learns they aren't the letters he wrote and realizes that Toni wrote the original love letter (by comparing Deborah's letter to Toni's handwriting). He races to her home, but is told that she left on a study abroad program aboard a ship that will keep her away for her senior year. Michael rushes to the dockyard after a brief scuffle with Steve, screaming his love for Toni. After shouting her love for him as the ship continues to sail away, he dives into the water, but cannot reach the ship. Toni also dives into the water, the lovers embrace in the water and kiss.