Simon wants to buy the perfect gift for Deena because its their three month anniversary, but it ends up consuming his time which annoys his friend, Nigel, who's visiting. Rod (Lucy's ex-boyfriend) is spending time at the Camden's home because his mother died and doesn't want to face his father as he's angry with him. Heather is back in town, and she tells Matt that she's engaged. Meanwhile, Dr. Hasting's---the doctor who almost killed Matt when he was born, works at Glen Oak Hospital and Annie is not thrilled, especially with the possibility that he may deliver her twin babies. Mary tells everyone that she's back with Wilson, but it's not true. She made it up to get attention from guys. Lastly, Michael Towner, who hitted Mary with his car two years ago calls her.

During a difficult labor, Annie asks Dr. Hastings for help. Lucy decides to break up with Jordan because she doesn't feel the same love for him as he feels for her. Simon continues to pray for twin boys. Happy is alone in the house causing some mess and trouble. Simon suddenly decides that he would ask his parent's if he could get his ear pierced. Matt is reluctant and scared about giving blood and also tries to calm everybody's tensions with the arrival of the babies. Lastly, Ruthie is the same as usual in this heart-warming episode; bad-mouthing the twins until they come.

Eric worries about Matt as Heather's wedding approaches. Eric learns that his sister Julie is dating Dr. Hastings (the doctor who delivered the twins and almost killed Matt at birth) without telling him or the family. Also, Lucy and Simon are both in their awkward love triangle between all of their two best friends and lovers. Ruthie wants to be a bridesmaid and a bride at Heather's wedding.

In the third season finale, Eric counsels an engaged couple facing difficulties. Mary, Lucy and Simon learn the repercussions of forbidden love, especially Simon when he is caught in his bedroom alone with Deena kissing near his bed. Julie gets married to Dr. Hastings (Hank) and learns that she's pregnant. Also, Heather breaks up with her fiance after she learns he was cheating on her with another woman. Matt tries to save his relationship with Shana after he ran off with Heather, and does this through his pleading of forgiveness.

The Colonel and Grandma Ruth return from being out of the country for six months. Simon surprises his grandparents with his new haircut. Matt decides to move out of the house and gets his own apartment with John Hamilton. Aunt Julie's new husband Hank gets Matt a job at his hospital working in the cafeteria. Eric begins to suffer a mild heart attack due to the stress from his job.

Eric and Annie put on their counseling hats when a very pregnant Julie appears on their doorstep prepared to leave her new husband Hank. Eric decides to take Hank out to dinner to discuss their issues. While they are at dinner, a very pregnant Julie goes into early labor. Unable to transport her to the hospital because Simon and Mary are out to dinner and Lucy is on a date, Annie does her best to calm Julie down. Hank and Eric return to the house just in time for the birth. Julie delivers a baby girl. Grateful for Eric's effort, Julie names the baby after him: Erica. Meanwhile, Lucy is disappointed when her date expects her to be 'the man', and Simon attracts the attention of an older female admirer.

Rev. Eric Camden counsels a sexually molested girl to help her express the rage and pain she's been hiding from her family. This dark secret that Mary knows about weighs in on her, which brings her to open up to Lucy. Meanwhile, Simon and Ruthie learn the power of communication with their friends and classmates. Also, Matt helps Hank reveal an important personal secret to Julie before his mother visits.

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.

Eric tries to arrange a romantic evening with Annie, but Annie keeps turning down every attempt he throws at her. At the same time, Annie takes Eric by surprise with the news that she would like to quit college and to start teaching to help get her out of her depression. Meanwhile, Simon is at risk of being fired from his new job at the pizza parlor by his excessive tardiness and discovering that waiting tables takes more people skills than he's equipped to handle. Also, Robbie sets Lucy on a date with one of his friends while Matt is concerned about a woman who keeps showing up at the clinic a lot. Lastly, Mary performs terribly in fire fighting training distracted by her consuming relationship with Wilson.

Lucy and Robbie argue over who should tell Mary about their emerging relationship. Meanwhile, Matt worries that a young woman in his study group might be a victim of physical abuse at the hands of her belligerent boyfriend. Eric's sister Julie shows up at the Camden house with her toddler Erica and annoys Annie as she tries to prepare a lesson for her class. Simon meets up with Sasha and they both try to catch up on their personal lives.

Matt and Eric meet with Rabbi Glass to discuss wedding plans, and Eric learns that he is playing a smaller role than he had originally planned. Annie prepared for fewer guests to attend the rehearsal dinner and gets very flustered when she does not have kosher food. Ginger and Charles are prepared to fly to Glenoak, but Charles get's lost at the airport. Simon gets angry when Matt asks Robbie to be his best man. Meanwhile, Ruthie tells Robbie that she wants his room for herself after Matt moves out. Ben proposes to Mary, but he gets an unexpected answer.

When Eric learns that he must undergo double bypass surgery, he calls a family meeting to share the news but loses his nerve at the last minute and decides the group should go bowling instead. His odd behavior surprises everyone, especially Annie who grows more concerned when Eric's brother-in-law Hank shows up unexpectedly. Meanwhile, Robbie pesters Kevin about helping him make a parking ticket disappear. Lastly, Lucy continues to question whether Kevin has ever been with another woman.

When a nasty thunderstorm rolls through the region and threatens to postpone Lucy and Kevin's wedding, everyone scrambles to make it to the church in time. Mary barely catches the last flight in and brings Matt with her. Chandler and Roxanne rush to pick up Ben and his mother who are stranded at the airport in Las Vegas, but tensions run high and a fist fight breaks out; and Matt gives Lucy some very special brotherly advice when she confesses to pre-wedding jitters.