Will and Jack can't wait to arrive at the house of two old friends who are known for their wild parties but they discover that the former party animals are now sedately raising an adopted baby girl -- and Will shocks Jack when he volunteers to test his shaky parenting skills by babysitting her for them. Elsewhere at a snooty yacht club, Grace believes that Karen is jealous of her romantic relationship with Ben but then later regrets taunting her.

When they are asked to read at the civil union of two friends, Will and Grace verbally spar over her self-serving, get-and-take attitude where Will is responsible for everything -- but what's really bugging him is the overwhelming feeling that Grace is behaving more like a wife than an old friend. Meanwhile, Karen tries to help a caffeine-addicted Jack get over a failed crush but he's so jacked-up on java that only a tough-love approach will work.

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.

When Grace frets that she and Will might drift apart like their similar friends, she impulsively buys an expensive piano which she hopes will cement their mutual bond and love for music – or at least give her an excuse to perform a lot of show tunes. Meanwhile, when Jack is dumped by his latest romantic interest, he vents his grief by writing trashy novels which instantly draw Karen's passionate attention.

Will & Grace try to lure Tina, Will's dad's mistress, away from Will's father by setting her up with another man. Unfortunately the only man available is Will's gay friend, Larry. Also, Karen buys a horse for breeding, but the stud is more interested in stallions.

While Will and Grace are feuding, Karen and Jack hatch a wobbly plan to patch up their differences about co-parenting a baby by tricking each one into attending the same child's birthday party. After arguing over who brought the better gift, the feathers continue to fly as the best friends fuss over their conflicting agendas.

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.

Grace's wedding to Leo leaves Will feeling upset over losing his best friend.

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.

Will decides to further his cooking skills by taking a class and invites Jack to join him in the kitchen but when Jack decides to include his new boyfriend, the gourmet attorney finds himself a sad single in a cooking class full of couples. Elsewhere, Karen's mother Lois returns to town, slightly unnerving her daughter and calling on Grace's thrifty design talents to help decorate her new apartment.

A birthday party for Will (who's 40 going on 37) is an uneasy celebration, thanks to a symbolic gift from his new lover that betokens commitment. The strangest present: a nude portrait of Will that's lacking in certain details.

Karen is finally forced to come to terms with her feelings for her presumed-dead husband when Jack surprisingly tells her he thinks she belongs with Stanley, not Malcolm.

The big day has finally arrived - Grace and James are getting ready for their green card wedding. To Grace's dismay, Karen takes it upon herself to ignore her wish for a low-key wedding ceremony and decides to arrange including hiring Hall & Oates.

Friends and family gather for the funeral of Will's father. At the reception everyone shares with Will fond last memories of his father, while Will's last memory of his father is not as pleasant. Marilyn helps him realize the changes needed in his life.