In the fifth season-opener, big changes are afoot in the Camden household this fall as Eric is distressed by the fact that his daughter Mary has opted to postpone college in favor of a little soul searching and the glory of minimum wage. Mary decides to buy a car. Also, Annie leaves Eric with a handful at home so she can complete her teaching degree. Meanwhile, Simon attempts to fit in with the treacherous terrain of high school, and Lucy looks forward to ruling the school as a senior. Lucy can't wait to start a relationship with Andrew Nayloss, except he hasn't come back from summer vacation yet. Meanwhile, Heather and Matt's on-again-off-again relationship threatens to be off-again--- permanently. Matt considers the pre-med track at college and Ruthie learns that she will have to spend another year with her despised third grade teacher, Ms. Riddle.

Mary, still intent on her independence, finds herself buried under a number of unpaid bills after losing her job at the pool hall. Meanwhile, ""The Colonel"" (guest-star Peter Graves) surprises Eric and Annie with an unexpected visit. Matt blames everyone but himself for his failing grade in organic chemistry class. Lucy enlists Simon to assist her with her Homecoming Queen Campaign to help him gain popularity in school, and Ruthie's prayers are answered when she's transferred out of her nemesis' class and into a prestigious private school.

Responsibilities fly out the window when Eric and Annie enjoy seperate nights out on Friday. Although the reverend can't find anyone to hang out with him, so he calls a bewildered Matt. Annie is conferring with a professor (guest-star Jeff Yagher). Mary strays even further away from her parent's image of her when she is tempted to drink and smoke one night after work. Also, Mary makes friends with married co-workers Frankie and Johnny (guest-stars Chyler Leigh, Nathan West) with questionable morals while working the late shift. Matt blows Simon's chance at a big date with an older woman (guest-star Katie Stuart) when Matt is distracted by a close encounter of the female kind and forgets to pick up Simon. Also, Lucy gets a taste of the not-so-glamorous side of parenting when her and a classmate take care of an egg.

Exasperation reaches an all-time high in the Camden household, as Eric and Annie helplessly watch their oldest daughter Mary and her worrisome friends continue to head down the path of destruction and into the hands of the law. When Frankie (guest-star Chyler Leigh) expresses interest in signing up for college classes Mary starts checking out Lucy's early application packets. Meanwhile, Simon has a hot date and Lucy gets a weird proposition from a classmate. Lastly, Ruthie discovers manipulative fun of keeping a diary--- much to the embarrassment of Eric and Annie when she sees them having SEX!

Tensions run high as a doubtful Julie lets Mary baby-sit Erica, only if Mary has no visitors. But when Frankie (guest-star Chyler Leigh) comes by and begs Mary to take care of her baby Mercy, Mary can't resist helping her. Then, Mary is then caught with an open bottle of beer while babysitting. Meanwhile, Lucy volunteers to chaperone Ruthie's sleep over and to watch the twins. Also, Simon is on a quest to change his image and does this by piercing his ear. Matt pursues a woman who wants nothing to do with him. Also, Eric and Annie clash with Mary's disreputable friends.

Still unemployed and bills mounting, Mary continues her downward spiral to rock bottom as Eric and Annie fight about how to effectively deal with her numerous lies and immature behavior. Meanwhile, the fear of what may happen to Mary starts to take toll on the rest of the whole family. By this, it is prompting the children to break open the twins piggy banks to help Mary pay her bills. To get the credit card company to stop calling, however, they are forced to make a risky decision. During all this, Mary CONTINUES to ignore her responsibilities.

Eric and Annie desperately try to figure out how Mary managed to pay her credit card bill while the kids team up to throw them off the scent. When the parents vs. children game finally breaks down, drastic changes happen. After learning that Mary stole from the twins to pay her bills, Eric and Annie come to the heart-breaking realization that they must take drastic action to help their misguided daughter and to protect and preserve the family. The Camden's gather to confront Mary with their feelings of hurt and betrayal and their conclusion to send her away to Buffalo with ""The Colonel"" and Grandma Ruth.

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.

Despite the disapproval from the rest of the family and his own hesitations, Eric takes in Mary's ex-boyfriend Robbie Palmer (Adam LaVorgna) to live with the Camden's for the night after learning that he's homeless. Matt also shows up unexpectedly after being kicked out of his apartment by John, who needs quality time with his girlfriend. Meanwhile, Mary calls home again and hears Robbie's voice on the other end and assumes he's dating Lucy now. Also, John proposes to his girlfriend Priscilla in front of Matt.

A month has passed since Eric invited Mary's ex-boyfriend to stay with the Camden's until he got on his feet. Robbie happily continues to act as a member of the household--- and it's driving Annie crazy. Robbie is Eric's latest 'project', Ruthie's new best friend, recipient of Simon's financial advice, and according to Mary, Lucy's boyfriend. He's even cooking and folding laundry (the wrong way!). Frustrated and emotionally strained, Annie starts to think nobody needs a mother anymore. Also, Matt also feels unneeded from the family due to Robbie and pays an unexpected visit to Heather and her new boyfriend.

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.

After their lackluster attempt at kissing, Mike (guest-star Jeremy Lelliot) and Lucy agree to be friends and to fix each other up on dates--- but the plan bothers Lucy more than she anticipated. Meanwhile, Matt's in a huff over John and Robbie's newfound friendship and feels slighted by the family. Eric also continues to feel alienated from his family when they keep going to Annie for advice. Also, Annie feels slighted when Ruthie plays an un-funny joke when the twins recognize her as their ""mama"".

Mary's feelings for Robbie resurface when she inadvertently finds out he has a secret date for Valentine's Day, and the whole family schemes to uncover the mystery woman. Meanwhile, with the exception of Lucy who has a date with Jeremy, the other Camden kids feel deflated when their Valentine's plans fall through and they end up stuck at home celebrating Sam and David's second birthday. Lucy and Jeremy's first date does not go as expected as they both keep on running into Lucy's ex-boyfriends. Although all's well that ends well by the end of the episode for everyone.

Although Robbie is just as nervous as everyone else, his presence in the house during Mary's weekend stay causes a great deal of concern among the Camden's. Matt and Lucy are especially suspicious after Lucy accidently finds a condom in a misplaced wallet. Imagine their surprise when they learn that the provocative prophylactic belongs to Simon--- who just so happens to be spending the evening with his new lady friend, Sasha.

Robbie is ecstatic when his long-lost father (guest-star Alan Thicke) who is a dead-beat dad appears out of the blue. Although, Eric and Annie distrust the dead-beat dad's motives. He also convinces Robbie to move out with him; against Eric's wishes. Meanwhile, Ruthie turns to Mary for advice on how to get around their parents rules when wanting to buy a makeup kit that they said 'no' to. Also, a very convinced Annie worries when Lucy starts having a relationship with her friend's freewheeling ""unmotherlike"" mom. Also, Simon develops a bad attitude with his mother when not wanting to do his school work, but wants to hang out with his friends.

Matt begins to go crazy over a psychological evaluation that he is required to take for his medical-school application. Matt also notices the strange demeanor of his psychologist, which leads to a surprising twist. Meanwhile, after Ruthie gets into trouble at school for missing homeroom classes daily, she tricks Robbie into coming to talk to her principal. Simon decides he no longer wants to be together with Sasha since they have nothing in common and that she is not that intelligent, but the plan backfires on Simon. Also, Mike wants to try to be in a relationship with Lucy again, but unfortunately she turns him down since they are both on the rebound from Jeremy and Elaine. Lastly, Eric must convince a terminally ill patient to embrace life no matter what the doctors tell him.

The striking resemblance of Robbie's new friend, Marie, to Mary raises eyebrows among discerning Camdens. Annie's invitation for her to stay for dinner makes things weirder for them. Back in Buffalo, unbeknownst to Robbie, Mary accidently bumps into her old boyfriend Wilson (guest-star Andrew Keegan) and his son Billy at the train station and makes plans to meet him for the evening. Mary is unsure on whether she should tell Robbie, but confides in her family about this. They all say that she should tell Robbie about this, but decides to ignore their advice. Also, Matt meets Robbie's ex-girlfriend, Cheryl, at the restaurant where she works. He starts to have feelings for Cheryl and tries his best to try to get her to go on a date with him. His efforts work by the end, but is having a hard time telling Robbie about his interest in his ex-girlfriend.

Annie discovers that the particularly flirtatious mother of one of Lucy's friends, Serena is seeing Eric for therapy sessions. Annie strongly requests that he refers her to someone else. Annie then has to deal with the guilt over her jealousy-induced interference between the two. Also, Simon is mortified when word gets around school over the fact that he's a virgin. Annie had shared the details of Simon's sexual inexperience with his ex-girlfriend's (Sasha) mother, Rita. Meanwhile, Matt struggles about telling Robbie he's interested with his ex-girlfriend, Cheryl. Lastly, Robbie is also hiding a secret from Matt that involves his ex-girlfriend Heather.

The Glenoak Community is making a big fuss over a petition that is protesting the apparently unfair firing of one of Ruthie's teachers, Mrs. Miller at her private school. Annie's father Charles drops by at the Camden's for a visit. Annie is then surprised and shocked when she she learns she has a half-sister.

Mary returns home back to Glenoak for the summer to spend some time with her family, but fears about being together again with Robbie. Eric and Annie are recipients of what may or may not be advances from unmarried acquaintances. Simon and Deena see that they still have feelings for each other, even though she has a boyfriend. Matt agonizes over telling his family about his new relationship with Cheryl, but soon decides to tell them all. Lastly, Lucy surprises herself and others when making a proposal to Jeremy and the possibility of going to college in New York with Jeremy. Although plans change when Mary, feeling rejected by Robbie, makes a shocking declaration.

Mary tries to right a wrong by explaining to Lucy that she never had adult relations with her sister's fiance. The only problem left is trying to convince Lucy. Wilson unexpectedly drops by the Camden home from New York to see if he and Mary are really over by finding out her answer. James talks to Eric about him attempting to have an affair with Annie as Serena comes clean with Annie about her trying to have an affair with Eric. Robbie and Wilson set aside their differences so that they can talk about Mary. Matt learns a few things when it comes to Cheryl's honesty when she doesn't tell her friends that she's dating him.