Simon persuades his parents to let him go to a party after they meet his friend, a senior who promises to look out after him. When he comes back home completely drunk, he puts his siblings in a terrible position on what do. Matt gets letters from two medical schools but he is hesitant to open them and they eventually end up with Ruthie. When Mary and Lucy take the same classes at an area college, they decide to go to a bar with Lucy's friends.

A startled Eric catches Mary and Lucy in the kitchen with Ben and Kevin in the middle of the night. The guys end up spending the night in the living room with Mary ad Lucy. Ben and Kevin's sister calls the house to inform Ben and Kevin that their mom is going out with a neighbor. Eric suspects that Ruthie knows a secret about Matt and Sarah and thinks they are married already. Meanwhile, an older couple seeks guidance from Eric when they can't seem to let go of their forty-four-year-old son, who has run away from home.

Matt and Sarah grieve over Eric's decision not to attend the nuptials following his argument with Rabbi Glass over Matt's conversion to Judaism. Hoping to patch things up between their fathers, Matt and Sarah seek their mothers' help in persuading them to put aside their differences before it's too late. Ben and Kevin come to Glenoak to meet up with Mary and Lucy so that they can resolve their problems. Robbie tries to figure out why Ruthie wants him to move out of the Camden household.

Against Eric's wishes, Simon asks Mrs. Kerjesz (guest-star real life survivor, Rita Zoharm) to tell her story about being in the Holocaust in his class presentation. To form a strong sisterly bond, Mary and Lucy decide to hate Matt's new girlfriend for no good reason and end up hurting her feelings and breaking up with Matt. Also, Annie suffers heartache when Ruthie tells her she ""hates"" her for making her clean the walls in her room after scribbling crayons on them.

In order to get extra credit, Simon volunteers to paint a holiday mural with a few good guys in his school. The other volunteers don't like Simon because they are inhaling paint fumes and are afraid he will report them. When one of the boys winds up in the hospital, Simon is accused of providing the paint. After he confronts the boy, the boy decides to confess everything to his parents. Meanwhile, Mary is suddenly thrilled about her community service after she meets the man of her dreams: Robbie Palmer. Eric and Annie are hesitant to allow Mary to pursue a relationship because of her punishment, but do allow Robbie to call her. Matt is up in arms when he learns that Shana is transferring to NYU and that his father provided a reference without his knowledge, and Ruthie wins first prize in her art-school project: a sculpture of the Camden family noses.

Ruthie is nervous when she finds out that Eric and Annie are heading to Scotland. She reveals a very unattractive side of herself when she openly admits that she's not about to sacrifice her own freedom and happiness to come home and be with her sick father. Kevin has a difficult time helping Lucy come to grips with Eric's illness; Sandy accepts Martin's marriage proposal just to get rid of her clingy boyfriend; and Kevin finds out a secret about Jane.

Mary tries to make Wilson say that he ""loves"" her, but Wilson thinks it's a big commitment and that they haven't known each other long enough to say those words to each other. Meanwhile, Simon and Ruthie are reading Matt's love letters to Heather and get caught. Matt tricks them by addressing one of the letters to ""Mrs. Matt Camden."" By this, Eric accidently finds the letter leading to think Matt and Heather got married over the summer, which worries himself, Annie and Heather's mom, Mrs. Cain. Lastly, Eric helps Lucy's friend, Laurie get closer to her mother.

Eric and Annie must deal with the emotional fallout as they learn about their kids tumultuous love lives. Mary upsets her parents by announcing that not only has she decided to skip college in the fall, but she is getting back together with Robbie. Matt is forced to choose between his girlfriend Shana (who has moved back to Glenoak for the summer) or his ex-flame Heather, who confesses that she still loves him. Lucy dates Robbie's cute brother Ronald, disappointing Andrew Nayloss who still harbors feelings for her. Also, Simon gets dumped by Deena and Ruthie takes advantage of her new boyfriend.

Matt's new girlfriend seems more interested in hanging out with his family than with him; Simon thinks he can make himself invisible; Lucy wants to join the cheerleading squad.

Eric and Annie decide to renew their vows; a widow seeks Eric's help to confront the juvenile who murdered her husband; Mary is reluctant to put down her crutches.

Eric and Annie try not suspecting the worst when they discover money missing from the church treasury and all the evidence points to Lou, the church treasurer. Later, they all find out it is for his disabled son who was kicked out of his home and needs to find a new one. Believing that Coach Koper has more than basketball on his mind where Mary's concerned, Matt and Lucy risk alienating their sister to discover the truth. Also, Simon lets the game of golf overwhelm his life and ends up breaking a lot of things.

As Annie plans a mysterious day of cleaning as Eric discovers the shocking news that Mary ran away from ""The Colonel""'s to come back home because of a devious scheme she had with Robbie and freaks out. Eric is convinced that more trouble is brewing and goes to insane lengths to find answers. In reality, Mary is heading home for a huge surprise birthday party for Eric, attended by all the people whose lives he's changed for the better in the past few years. Chores at home are interrupted, however, when Ruthie discovers Frankie and Johnny's baby, Mercy at the Camden front doorstep. Meanwhile, Lucy stays with her friend Mike's (guest-star Jeremy Lelliot) near catatonic mother for the day, and drops a proverbial bomb on Lucy. Also, Matt and Simon try to figure out why they delivered Mrs. Bink (guest-star Eileen Brennan) to the hospital.

As Annie begins teaching, she inadvertently gives a student some bad advice. At the same time, Eric and Annie painfully discover how much their constant arguing is affecting the family. Lucy and Robbie finally face up to their feelings after she intentionally sabotages one of his dates out of jealousy. Cheryl goes to Eric for some guidance in her relationship with Matt, but she misinterprets the reverend's input in the matter. Simon is attracted to a girl who is dating one of his friends. Mary is left to mull over Wilson's marriage proposal and it's even more confusing when she has a romantic encounter with a fellow firefighter trainee who shows an interest in her.

Annie is livid when her father brings along his girlfriend on a weeklong visit; Mary and Matt pursue new romantic interests; Lucy wants to find out if blondes really have more fun.

One of the members of Eric's congregation, Mrs. Bink persuades him to investigate the real reason of why her best friend Mrs. Hinkle is moving into a retirement home. Meanwhile, Simon and Ruthie are performing an experiment and are trying to convince Matt that Simon is shrinking, but the tables suddenly turn for Simon. Also, Lucy tries to get to the bottom of one of her classmates, Shelby as she is rumored all over school of being bulimic.

Simon becomes emotionally involved with his best friend's sister, Karen who's a gang member. Meanwhile, in a show of independence Lucy dons makeup and revealing wardrobe with her friend's to meet guys at the mall and gets caught by Annie and Ruthie. In addition, Ruthie questions the speed of light to everyone in the family.

Lucy gets an invitation to have pizza with two rebellious friends, then blames herself for the tragic car accident that claims her friend's life, and her sister in the hospital. After Lucy's friend is killed, the family rallies around her, noticing her unusually distant behavior. In addition, Mary does a favor for her ex-boyfriend Wilson and baby-sits his son Billy so he can go to his prom. Also, Simon gets his own room while Matt moves into the attic.

Annie's father Charles shows up at the Camden household for a weekend visit as Ginger supposedly needs to get away for a bit. But Eric forgot to tell his wife about it and nearly everyone in the Camden household is too busy to spend time with the elderly man. So Grandpa Charles takes Simon to get his learner's permit for driving and they end up being the center of a televised police-pursuit. Eric lies to Annie about his plans for the day, which include a trip to Glenoak Hospital.

Matt and Sarah argue over their wedding plans and their agreement to forego buying an engagement ring and seek Eric for advice, who isn't happy with Matt for getting engaged in the first place. Because of Eric, Matt buys Sarah a fake engagement ring. Mary and Lucy fly to Buffalo for a weekend, or at least that's what Lucy thinks as Mary makes plans of her own. At the airport, Lucy meets a police officer who invites her and Mary to double-date with him and his brother.

Strenuous events impact all the Camdens as Kevin and Lucy cope with an unexpected tragedy in their young lives. Matters worsen when Lucy convinces her father to let her deliver next Sunday's sermon while she is still in an emotionally unstable condition. Martin frustrates Sandy by suggesting that they get married and build a family for their infant son, then becomes angry when he realizes why Sandy is really holding back. Ruthie is studying in Scotland for the time being, and Annie can't shake the feeling that something is terribly wrong with Eric.

Eric enlists the help of a neighbor to stop Matt from smoking, and makes a vain attempt to help Lucy deal with her flowering womanhood.

Mary undergoes knee surgery, while Matt learns that Michael Towner was the hit-and-run driver; Wilson reveals the truth about Billy to Eric.

In the third season-opener, Annie is feeling a little depressed since she's 3 months pregnant. Ruthie is pretending to feel a little pregnant herself. Lucy is following the dating advices from 'The Rules' book she has. Matt moves in an apartment with three attractive girls. Eric is looking for the perfect 20th anniversary plan for Annie. Mary gets a lot of attention from guys, which makes Lucy jealous. Although, one of Mary's 'guy' friends asks Lucy out. Matt finally comes back home because of girl problems he was having with his new roommates. Simon's girlfriend is acting a little weird. Eric and Annie tell the kids they're having TWINS!

Mary's future may be resolved, but the rumor mill surrounding her situation runs rampant. While ugly rumors spread about Mary's sudden departure, Simon is persuaded to use his sister's bad reputation to boost his 'cool' quotient at school and gets into some trouble of his own with identical twin bad girls, Carol and Sue Murphy (Mary Kate and Ashley Olsen, Full House). Congregational gossip irks Eric. Lucy wrestles with high school hearsay. Ruthie spreads phony tales to draw attention away from Mary, and Matt's infatuated with a beautiful stranger. Also, Annie goes out with an old boyfriend.

Kevin goes all out to create the perfect romantic setting for Valentine's Day. Lucy doesn't wanna attend because she had him agree not to propose on Valentine's Day. Eric and Annie convince Lucy to go. Kevin invites all the Camdens, his brother Ben and their mom to be there with him when he finally gets down on one knee to propose to Lucy. Meanwhile, Roxanne overhears Chandler practicing his own proposal to her but she asks him to wait so they won't steal Lucy and Kevin's thunder.