When Grace receives an unexpected marriage proposal from her boyfriend, Will tries to be supportive of her decision but finally tells her that she's making a mistake, even though he's putting their friendship at risk. The situation is complicated by interference from Grace's socialite assistant, Karen, and Will's outrageous friend, Jack.

After Grace defies Will's wishes and brings home a puppy, Will can't resist the pooch and begins to treat him like a newborn baby. Meanwhile, Jack and Karen worry about the dog's effect on Will and Grace and insist that the new parents go out for a night on the town.

Will finds a "substitute Grace" in Val, a new neighbor who is available for plans with Will while Grace is consumed with work. As Will and Val continue to spend more time together, Grace fears that she has been replaced and fights with Val to regain Will's attention. Meanwhile, Jack seeks support from Karen after the court finds him guilty of slapping a meter maid and sentences him to pick up trash.

When Rob and Ellen admit that they don't have fun playing games with Will and Grace because of Grace's competitive nature, Grace works to change her image. However, as Grace loses her competitive edge, Will's emerges and he convinces his partner to care only about winning. Meanwhile, after learning how to administer CPR from Jack, Karen saves a workman's life.

Despite her moving out (to across the hall), Will still feels that Grace clings to him, so she asserts her independence by having a dinner party without him. Meanwhile, to keep the INS at bay, Jack is forced to move in with Rosario.

Tired of Rob and Ellen's low-rent taste in dining, Will and Grace start hanging with a pair of hip downtowners they meet at a sushi joint. But as the new pals paint the town, Rob and Ellen see red when they catch their best friends lying to avoid plans to dine at their favorite eatery: a coupon-crazy Italian chain in Secaucus. Meanwhile, Jack's inner child gets a little pick-me-up when he joins Karen at a PTA meeting at her kid's school.

When Rob and Ellen ask Will and Grace to be the best man and maid of honor at their wedding, Grace's sexy past with the groom is exposed when Ellen learns at her bachelorette party that Grace once slept with Rob. Meanwhile, Jack is confused by his reaction to the entertainment at Rob's bachelor party.

In a flashback to Thanksgiving 1985, coed Grace invites her college boyfriend Will home to meet her family, but their romantic relationship swerves dramatically when a conflicted Will phones a teenaged Jack for some crucial advice. Unfortunately, Will and an angry Grace end up temporarily estranged when he blurts out the truth and she orders him out of the house -- and her life.

Grace's lousy poker playing leads Will's friends to ban her from the game, but Grace makes an amazing turnaround to stay in; Karen uses a snippy socialite as a guinea pig for cosmetic surgery.

Will and Grace feel they need more elbow room, so they search for larger digs and find an exquisite place—despite the efforts of Sandra Bernhard—but to finance the move, they illegally sub-let their old apartment. Meanwhile, a well-intentioned Jack begins filming a documentary of Karen's colorful life to celebrate her birthday but accidentally stumbles upon her estranged, lowlife mom.

After Will and Grace move into their expansive new dream apartment, they discover the awful pangs of separation anxiety as they pine for their smaller old digs now happily occupied by their friends who sub-let the place. Elsewhere, Jack tries to reconcile Karen with her estranged grifter of a mom, who wants to recruit her daughter for her next caper.

Grace and Leo impetuously take their vows at a Central Park wedding that is a ratings stunt hosted by Today's Katie Couric. Grace's pals, especially Will, are hurt that they weren't invited, but all seems forgiven when everyone including Grace's outspoken mom and the subdued Mrs. Marcus gather days later for a swank reception. It should be a festive bash, but the emergence of unsettling details about Leo and about the park nuptials give Grace reason to wonder whether she has made a mistake.

Jack suffers Karen's wrath when he is seduced into friendship with her manipulative British romantic rival, who has set up house with Karen's ex-husband. Meanwhile, Will and Grace try to re-connect their lagging friendship with a competitive night of board games with their friends.