Carrie is gearing up for the biggest night of her life - her book-launch party. Naturally, Samantha serves as Carrie's publicist and party-planner. Miranda, who's back in the office and loving it, gets a timely call from her pre-baby ex-lover, Walker Lewis. Excited by the prospect of a replay of their one-night stand, she invites him to be her 'plus one' for the party.

While discussing the party particulars with her punchy publisher, Carrie meets the charismatic (and cute) writer, Jack Berger. After a flirtatious fast-food meal on a park bench, Carrie dares to invite Berger to be her 'plus one' for her party, but her hopes are shattered when Berger casually mentions he has a girlfriend.

Carrie tells the girls that she 'sparked' with Berger and laments the fact that he's unavailable. Miranda admits that she purposely neglected to tell Walker she has a baby. After discussing the whole 'plus one' problem, Carrie starts thinking about what she has (a job and an apartment) and what she doesn't have (a boyfriend). She wonders why we let the one thing we don't have effect how we feel about everything. She asks: Why does one minus a 'plus one' feel like it adds up to zero?

Samantha decides to splurge on a chemical peel to prep for the book party and emerges looking like an overripe tomato. Charlotte prepares for the party by bedding country club-ready Justin Anderson the third, her 'perfect plus one.' The scene is perfect until Bunny barges in spewing accusations and Charlotte is left minus one.

Carrie soaks in the glamorous party in her honor and thinks 'Who needs a date? - until she spots Berger sans girlfriend in the crowd. It dawns on her that she's lonely. Miranda, on the other hand, has lured Walker back to her home. However, when Brady's cries interrupt them mid-climax, Walker walks out. Miranda takes Brady in her arms and realizes that she's not the same person - she's plus one. On the way home, Carrie's driver reminds her she's got something to celebrate. Spirits lifted, Carrie realizes she likes knowing that there are men out there who can still give her that 'spark.'

Carrie tells the girls that she's headed to San Francisco for her book tour and that she is desperate to get laid. And well, yes, she just might call upon Big while she's there. She recruits Samantha to join her on the journey West - by train. Feeling jaded by NY and NY men, Samantha is up for the adventure. Carrie wonders: "Are we the new bachelors?"

Charlotte gets a surprise visit from her bald, sweaty lawyer, Harry, with divorce papers in hand. Harry invites the new divorcee to view a swanky bachelor's apartment that is about to go on the market. At the apartment (complete with bedroom strobe lights and surround sound), Harry blurts out that he finds her incredibly sexy. The old Charlotte is taken aback but the new Charlotte jumps him. She confides in her gay pal Anthony that she had incredible sex but that she has no interest in being Harry's girlfriend. Anthony congratulates her and gives her the lowdown on the rules of 'hot sex' and nothing more.

Back on the railways, Carrie and Samantha are nowhere near hot sex. Even crashing a bachelor party in the bar car turns up nothing but happily married men. Samantha nurses her wounds with a bottle of champagne while Carrie obsesses over the inopportune arrival of a giant pimple.

Arriving at her book reading, Carrie finds herself in front of an audience more excited about the next star reader, Mr. Winkle the dog. During the Q and A session, Big emerges from the crowd and asks her if the "Big" she writes about has a name. Carrie coyly tries to lure Big to bed but he's more interested in understanding what she wrote about him. He tells her he doesn't want her to get hurt again. Despite Carrie's insistence that she's fine, Big goes to bed with her book, not her, on top of him.

Meanwhile, Charlotte is back in bed with her lawyer and practices the art of 'just sex' - sending him on his way with no romantic talk when they're done. Carrie has given up on any sex, but by morning, Big is back to himself, joking that she'll need more material for the sequel.