Bobby's a bartender and the only son of gregarious, salt-of-the-earth Irish Catholic parents from Boston. His fiancée, Liz, is a toney Harvard student and she's Protestant (no, that's not the problem). Liz has two dads, not one, and they're a worldly pair of well-heeled gay men.
Bobby and Liz break the news of their secret engagement to their families and each gets a less than warm response. In fact, Bobby's conversation with his folks ends with him moving into Liz's parents' guest house. Naturally, this doesn't thrill Philip and Simon, but at the risk of losing Liz completely, they agree to the situation temporarily until Bobby can work things out with his parents.
When Liz observes Bobby encouraging a friend to lie in order to break up, she questions his sincerity in their own relationship. In order to prove that he's changed and that he really loves her, she challenges him to find all the women he's dumped in the past and tell the truth about the break-ups. But Liz's plan may backfire when Bobby reconnects with the seemingly "perfect" girl.
Now that Bobby has moved into Liz's parents' guesthouse, he's been warned that neatness counts – a lot! But his attempt to make coffee with Philip's fancy cappuccino machine leads to a burst pipe in the kitchen. In desperation he calls his dad, Mace, to help fix the calamity before Philip gets home.
When a client unexpectedly gives Philip tickets to a Red Sox game, Bobby sees it as an opportunity for family bonding and convinces Philip and Simon to invite Mace. But Mace's idea of how to watch a ballgame is quite different from Philip's and Simon's. Meanwhile, Liz tags along with the O'Neil women to a basement sale that's more like a battlefield.
Mace learns a lesson about stereotypes when he takes ill and is treated by a doctor who happens to be gay. Philip learns a similar lesson when his longtime friend and party planner, Joffrey, makes his own startling confession. Meanwhile, as their Halloween party approaches, Philip and Simon disagree about continuing their long-held traditions, and Liz wants to shed her "cute" image.
When Uncle Paddy O'Neil passes away, Liz offers comfort and support to Bobby by attending the wake – even though she's never seen a dead body before. In her angst, she forgets to drop off the key to the bar for the fill-in bartender and calls upon Simon and Philip for help. Meanwhile, the O'Neils return from the wake to find Philip and Simon hosting a karaoke challenge, which infuriates Mace – until he sees the day's receipts.
Philip and Simon initially oppose State Senatorial candidate Charlie Carson's plans to tear down an historical theatre, while Mace supports the politician's plan to build a hotel in its place. But Mace questions his support when he learns that Carson supports gay marriage, which causes Philip and Simon to change their minds and support him. When a dead swan threatens to land the candidate in hot water, Philip and Mace try to help him resolve the messy situation, but soon regret their decision when an attractive, young intern pays the candidate a visit.
In an effort to get their families to join in the celebration of their upcoming wedding, Bobby and Liz convince their folks that the other's family is throwing an engagement party. Instead of working together, the families get competitive and try to outdo each other – which causes Liz and Bobby to flee to Vermont in frustration. Afraid that the young couple has eloped, the parents embark on a road trip to stop them – but a road trip with Mace and Philip is anything but a smooth ride.
Thanksgiving turns into a fiasco when Liz invites Mace's overbearing mother, Colleen, to the dinner. A web of deception begins when Mace tells the very conservative Colleen that Philip and Simon are Liz's uncles – instead of her dads. As luck would have it, Colleen is so charmed by Philip and Simon that she wants to introduce them up to her unmarried daughter. Meanwhile Philip spins a tale of his own when he tells his stuffy decorator that Liz's future in-laws are wealthy. But it all goes awry when the designer pays a surprise visit during dinner to meet Liz's future in-laws.
When Audrey shows up with an unusual abstract painting that everyone agrees is awful, Mace sells the painting to Philip while she's away. Philip has good luck in selling the painting at his gallery, but when Audrey learns of the transaction, she's furious and demands that Mace and Philip get her painting back. What they have to do to get it back from the blind man who purchased it is anything but pretty.
Bobby and Liz's families are trying their best to blend their very different styles of celebrating Christmas when a Christmas Eve delivery to Philip and Simon's house injures "Santa" Mace. And Bobby feels pressure to compete with the lavish Christmas gifts that Philip and Simon have planned for Liz.
Bobby is furious to learn that Liz has discussed their sex life with her dads. While Mace and Philip are pleased that the relationship could be in trouble, Simon and Audrey conspire to keep the couple together.
Philip hires Mace to pose as a typical American couch potato. But when he grows tired of eating chips and watching sitcoms while on display, it's left to a famous television personality to take his place (Ed McMahon). Meanwhile, Audrey and Simon become best buddies while working together to create a recipe for the perfect sauce.
When Simon asks Audrey to make costumes for a small musical theater production benefiting gun control, Mace is furious to find out that she is involved with the show at all. But when both of the leads have to be replaced at the last minute, Audrey and Philip can only hope for the support of their own leading men.
Mace's longtime friend, Dan, visits for a planned fishing trip, but before the fishing fun can begin, the two men have old scores to settle. Meanwhile, Maddy has eyes for Simon's new teaching assistant but fears that he may be out of her league. Simon concocts a plan to make the seemingly unlikely love connection.
When a TV show plans to air a "Where Are They Now?" special, the O'Neils discover that Simon used to be a member of an 80s one-hit-wonder boy band. Mace, desperate to become president of the local merchants association, promises that he can reunite the band for the Valentine's Day Winter Carnival. As Mace and Simon are consumed with the band's reunion, Audrey and Philip's Valentine's Day hopes are cast aside. And Bobby panics when he can't come up with an original plan for a special Valentine's Day with Liz.
When Audrey expresses concern that Liz and Bobby are "living in sin," both families weigh in on making immediate wedding plans, but the accelerated pace could be too fast for Bobby. Meanwhile, when Philip learns that Mace is related to a famous playwright, he begs Mace to help him gain entry to an elitist, social club on.
Philip's plans to view the Oscars are spoiled when Mace accidentally breaks the remote control. Their desperate attempt to get the remote fixed lands them in the emergency room with a nurse who certainly wouldn't win any awards for her bedside manner. Meanwhile Simon teaches Audrey the fine art of "dissing celebrities" on the red carpet and, to her own amazement, she unleashes a hidden talent.
Thinking that they're a little fragile for the wilderness, Mace is less than welcoming to Philip and Simon when they all attend Bobby's camping bachelor party. But a sexy park ranger helps Philip and Simon even the score.
A family outing to a department store to register for wedding gifts becomes traumatic for Philip when a piece of the china set is unavailable. But Dr. Bob, a famous television psychiatrist who's signing books nearby, comes to the rescue. Meanwhile, Bobby bonds with other fiancés who feel excluded from the gift registry process, and Mace and Simon's attempt to assemble a piece of furniture goes well – almost.
Liz and Bobby's adoption of a stray dog sparks a debate between the families on parenting styles. The O'Neils flashback to their strict disciplinarian ways with Bobby and Maddy, while Simon and Philip flashback on their gentle, nurturing approach with Liz. Bobby and Liz realize that they may have to compromise on some important decisions once they become parents.
A fight erupts between families over the text of Liz's and Bobby's wedding invitation -- specifically, whether or not to mention Philip's and Simon's sexuality. Meanwhile, Bobby's priest, Father Joseph, tries to talk Liz out of the marriage.
