Matt, Mary, and Lucy make plans to get away from the family for Thanksgiving, but when Eric's sister Julie comes to spend the holidays with them, plans are changed. After the family finds out about Julie's dangerous secret--her drinking problem--everyone decides it would be better to stay home. Eric decides to help his little sister overcome her problem at home rather than seek professional help--whether she wants it or not. Annie is not comfortable with the situation and is only concerned that the children stay safe after an unfortunate altercation between Julie and Simon.

A visit from Eric's parents, strict Marines colonel John and his equally military wife, strikes controlled terror among the grandkids, and even Jimmy Moon, who initially discarded Matt's accurate imitation of the usual boyfriend-grilling. They come to present George, the charming, manly boy they adopted from an orphanage. But Eric discovers detective Will Grayson, whose death was faked in a witness protection program, is back in Glenoak after the crime king's death in prison. He claims his son, none other than George, back, as remains his legal right. After a fugue attempt from George, a creative compromise is devised. Matt meanwhile discovers aunt Julie is on the verge of an alcohol relapse.

Simon is deeply hurt because pa didn't tell him his girlfriend Deena behaves so moodily because of her annual leukemia check-up, yet handles her admirably. Matt discovers aunt Julie has moved in town and taken a teaching job. She rudely keeps him and later brother Eric at arms-length, resenting obvious concerns for her alcoholism problem. Fake tears' success on the DMV examiner success inspires Mary to abuse crying regularly, to nobody's ultimate profit.

The whole Camden family is invited to Matt's deaf ex Heather's wedding to Mason, celebrated by Eric. Matt brings current girlfriend Shana, yet ends up convincing the bride to leave the groom at the altar and drive away together. Wile his ex Lucy flirts with Joe, Jordan gathers the courage to tell her he's dating Mary. Simon is confused after being kissed by Deenah's cahoot.

Matt brings unamused Heather, who hoped he would propose again, back to church, where he exposes after some hesitation groom Mason's flaw, while desperately trying not to lose 'abandoned' Shana. Simon learns the kiss was a 'love test', which is rewarded with more, and Jordan encourages to just enjoy it without excessive worries. Jordan tells Lucy, who out of mere jealousy makes out with wedding guest Joe. Eric has a hard time accepting Julie's sudden announcement to marry Dr. Hank Hastings, but doubts soon shake that couple to be.

Mary and Lucy selfishly make Matt feel 'guilty' he hasn't moved out yet, although Annie still hopes to keep him home in a garage apartment. They even get Hank to find him a menial morning job in the hospital cafeteria. But Simon feels desert when Matt takes an apartment with John Hamilton. Eric and Annie worry about the Colonel's attitude to Julie's marriage, but the grandparents have gone soft after an around-the-world trip, as George's crazy hairstyle illustrates. But the stress gives already-overworked Eric a mild heart attack.

Simon sees no harm in accepting a 'non-date' with Diane until his girl Deena and her pa see them in the pool-hall. Lucy's joy to get her drivers license is spoiled by the silly picture. Cute, car-less Andrew Nayloss's proposal to pick him up for a movie cheers her up, but he expects the whole courteous, generous treatment girlfriends usually expect, plus a grilling from his dad. An apparently stray kitten seems to choose Ruthie to provide a home, but after lots of hiding the truth catches up. Matt tags along when Eric comes to hospital and takes Hank to dinner to discuss why pregnant Julie is with Annie, jealous about the gynecologist's female patients, including a supermodel. Thus they are out of reach when contractions start weeks early.

After Eric is approached by a mystery girl he can't identify, who won't tell her problem, the Camden parental paranoia extends to preventive preying, so the kids assume one of them must be in trouble. After Lucy launches the theory her siblings may invent colorful friends to 'test' their own fib stories, pointless palavers abound. Simon proves his funny classmate Luke is real, Mary is keeping an outsider's secret. Hank blames Matt for his marital crisis just for accidentally giving jealous aunt Julie the impression Hank shares a secret with Matt, who thus gets a wealthy lodger on top of his roommate till further notice.

High school freshman Simon desperately looks for a new image, but clothes nor hairstyle do the trick, so he ends up with an earring. Matt is puzzled when a girl he approaches in the library calls her brother's help against him as 'stalker' after hearing he once dated Heather. Mary breaks every rule and promise when babysitting for Hank by taking in Frances's baby so her 'friend' can spy on Johnny, but the Camden parents' pool night just there makes the real, for all concerned unpleasant difference when Eric blindly assumes Johnny to be an abusive adulterer, while Frankie rather trapped him.

Irresponsible 'adult' Mary fails to realize how deep she's sinking, but both parents and siblings piece together from various sources she's about to hit rock-bottom but have no idea how to help? Eric can barely keep Annie from intervening directly before they know everything. The kids decide to 'borrow' enough from the twins' full piggybanks to cover her debts, but creditors seeing cash convince her to 'refinance, which would mean even more interest.

The monthly day when the twins' piggybacks are enriched with §10 is ahead, so the siblings fear the game is up unless Mary manages to repay the 'loan', but now her debt is reshuffled she idly spends her days in the movie theatre. So the Camden parents soon learn the dreadful truth they already dreaded. After pondering how to help her, a family intervention proving she's still in haughty denial, the last resort is packing her off to Buffalo, to be taken in hand by the Colonel.

Eric threatens Robbie with eviction because he thinks he's keeping secrets about Mary. The house is abuzz with secrets and preparations for an elaborate surprise party for Eric's birthday. Johnny drops Mercy on the Camdens' doorstep after Frankie abandons them. Mike trusts Lucy enough to look after his mother for a day, during which the woman surprises her, both by speaking and by what she says.

Robbie and Lucy gather the courage to tell everybody about their affair, only to find they all knew and don't really care. Without the thrill of sneaking, their first date fizzles. Ben Kinkirk and Mary both pass the firefighters course, but their meeting on whether to celebrate with classmates messes up Mary's reconciliation with fiancé Wilson., and Billy's questions make Wilson decide against her plan to elope. Matt discovers that Hank and Julie are planning a divorce, and Eric and Annie try to find out why and see if they can help fix it.

Preparations for Matt and Sarah's wedding are being made and things aren't going the way Eric or Annie planned. Matt decides he will convert to Judaism after a discussion with Sarah's dad who convinces Matt that he can convert on the wedding day much to Eric's dismay. Annie panics when Sarah's mother tells her to expect 100 kosher guests to her backyard pot luck dinner. Ruthie and Simon begin to resent Robbie being in the house. Ruthie wants her bedroom back forcing Robbie out now that Matt will be moving out and Simon gets upset that Matt chooses Robbie to be his best man and Sam and David call for Robbie instead of him. Lucy gets upset that Kevin won't come to Glen Oak for Matt's wedding and Ben decides to propose to Mary after Mary starts giving him the cold shoulder. Eric and Sarah's dad the Rabbi go head to head and it seems Matt and Sarah's wedding won't go ahead after all.

A big storm interferes with Lucy & Kevin's wedding plans. Kevin's family and many of the guests have trouble getting to the church.

Lucy and Kevin look for their first home as does Chandler; turns out they are looking at the same place. Eric and Annie decide to buy their house from the church; Ruthie plans to move into the garage apartment when Lucy and Kevin move out.

Matt takes Lucy shopping so that she is out of the house. Annie prepares for the baby shower while she is gone. At the store, Lucy goes into labor. Matt & Lucy are stuck in an elevator. Lucy gives birth to a girl.

The mixed joys of fatherhood way heavy. While Annie tends to the flu patients, Eric feels no better after learning that the haughty Colonel sired him before marriage. Martin's dad needs all his paternal love and self-control to patiently push the boy to step up to his upcoming paternity. Sandy's parents tell the Reverends to butt out, then refuse any responsibility for Sandy and disown her. Martin discovers an excellent reason that Ruthie shouldn't date Jack.