Simon isn't amused that Rose pulls all the stops out hosting a luxurious dinner to impress her Italian ex, Umberto 'Bert' Lanzo, who left her at the altar. He jests about wanting her back, or is he serious - and who is the mystery girl Simon agrees to talk to immediately but covertly? The Camden parents, are not amused that Ruthie's long-awaited cellphone does nothing for her social life. Eric urges the boys to call her, helped by unwilling Peter Petrowski's dad George 'Vic' Vickery and Kevin. Benjamin Bainsworth, meanwhile, finds her number and works up the courage to call after a year.

Annie loathes receiving an invitation to Simon's 'disaster' wedding to Rose in May, until she realizes that's the same day as Matt and Sarah's med-school graduation. Neither group will even consider another date, arguing that the other event is less important or troublesome. Ruthie considers taking a summer poetry course in Scotland to be with her ex Peter, but Eric won't pay and the phone-bill hits hard. Kevin plants the romantic idea of eloping. Rose's jealous ex Bert grills Simon about his mystery girlfriend and questions his commitment; Annie finds out and teams up with Bert, who talks Rose out of eloping as the Camdens would ruin this by attending. Yet the changes of plans and the truths that turn up inspire surprising changes of heart.

The wedding preparations inspire Eric and Annie to reminisce about their children's childhoods; Rose tells Simon she's late and he prays as passionately to make the right decision about starting a family as he once prayed to get a dog; Simon is disappointed that hardly anybody wants to attend his wedding and Rose somehow blames Umberto and keeps his doubts alive while her divorced parents, between blaming each other for everything (as usual), fear it's a "shotgun wedding"; at the rehearsal dinner, Ruthie meets charming teenage waiter Paul from Edinburgh.

Annie and Eric are delighted with Matt and Sarah's surprise visit in time for Simon's wedding--and not just because they announce they're expecting. Simon is relieved that he and Rose aren't expecting, therefore marrying purely for love; but the next minute he gets cold feet, at which Lucy eagerly pokes. More visitors, like Matt's one-time bride-to-be Heather, stir further reminiscing and speculations; Rose's ex Umberto even asks Eric's permission to sabotage the wedding. The big day is full of surprises, including from Matt and Carlos.