In this installment, we learn that change is gonna come for some key characters in “Mad Men.” But others — not so much.

SPOILER ALERT: Stop reading now if you haven’t seen “Field Trip,” episode three of the first half of “Mad Men’s” final season.

Matthew Weiner warned us that the scripts in these seven episodes of season 7-A would be densely packed, and he wasn’t exaggerating.

“Field Trip,” written by Heather Jeng Bladt and Weiner and directed by longtime series d.p. Christopher Manley, was overflowing with great lines and moments. But overall it felt like a more subtle delivery in many respects than in the first two episodes. Jon Hamm’s performance was incredible, even by his mile-high standards, and Jessica Pare and January Jones were right up there with him.

Had the Don-Megan and Don-returns-to-the-office moments not been so powerful, I could write 800 words on Betty. Weiner built the anticipation for her return by keeping mum about her over the first two episodes, and then in hour three unleashes a big storyline with the Betty we’ve come to know and hate.

The witch is back, twisting the knife in her kid’s gut, wallowing in self-pity, narcissism, jealousy and the status-conscious scheming that maybe her ugliest trait of all. Actually, her ugliest trait (setting aside the damage she inflicts on her kids) is how mean she is to people she deems inferior. Loretta the new housemaid/nanny should hit the road quick if she knows what’s good for her, no matter how fond she may be of “little angel” Bobby.

We saw ugliness on display in unexpected quarters this episode — from Peggy and Joan as Don Draper tried to make at least one of his attempted comebacks in this episode a success. Interesting to see how both of the top women at Sterling Cooper feel threatened by his return, even though he’s been a champion of both over the years.

Joan is a party to the craven move of presenting Don with terms of his reinstatement that are clearly designed to make him miserable enough to quit. And they do this even after acknowledging that Lou — Don’s ill-tempered, tin-eared successor — is “adequate” while Don is a “genius.” That’s some office politics right there.

As great as the office storyline was, as much as Betty got my blood boiling, this episode belonged to Don and Megan. Their telephone exchange after the blowup in L.A. was such a painfully real conversation. You could feel the glimmer of false hopefulness in both of them that they might work it out, even though it looks like they’re bound to break up. You can tell this episode was directed by a cinematographer because the direction was not showy in the least but so effective, especially the back-and-forth on that telephone scene, awkward pauses and all.

In the brief L.A. scenes, Megan’s remark about him pulling her out of a bathtub with slit wrists is sure to add fuel to the fire of conspiracy theorists who are sure that Mrs. Draper is about to be hacked to death by Manson family members. I don’t buy it, but after this episode, I’m thinking Megan is headed toward a “Valley of the Dolls” ending — which would be appropriate for a frustrated actress, then and now. (And it might satisfy the conspiracy buffs as Tate did co-star in the movie version of Jacqueline Susann’s famed trashy novel.)

Yet you have to admire the way the story turned on a dime with Megan. First she’s acting crazy around town in L.A., stalking directors and making public scenes in such a way that her flamboyant agent, Alan Silver, feel the need to ask Don to help settle her down. But when Don swoops in and finally comes clean to her about his own situation, Megan has no trouble thinking clearly about what his choices during the past year (or maybe nine months or so) mean for their relationship.

“I’ve been good. I haven’t even been drinking that much” is a line I never thought we’d hear coming from Don. But his honesty is too little, too late. “With a clear head you woke up every morning and decided not to be with me,” Megan replies. Hot damn, she’s right. I think many of us are happy to see Don still trying to fight for Megan, even if it is a losing battle, and still trying to fight for his position at Sterling Cooper, even when he doesn’t have to. He has a soft landing in his pocket (literally) from a bigger rival agency.

But Don wants more than money and status in the clubby Madison Avenue world. He wants his dignity back. That’s what made the office scenes visceral, as he learned just how much further he still had to climb. Walking back through the double-glass doors was just the first baby step. Hanging out with the office-less creative execs like Ginsberg et al. while he waited for the other partners’ verdict was humbling and eye-opening for Don. The youthfulness of the young execs was reinforced by to Don when one of them is pouring his heart out about his romantic woes, putting Don the role of the wise elder.

While all this is going on in Manhattan, somewhere in upstate New York a bra-less elementary school teacher is just waiting to torture Betty with her sunny smile. But first we catch up with Betty in a scene sure to please hard-core fans. Francine! She’s back! In a day-glo orange paint suit! And she works three days a week as a travel agent, but has ambition to get into real estate. And whaddya know, she’s still married to Carlton.

January Jones is great in these scenes. Her jealousy and contempt for Francine grow as she talks about experiencing the first pangs of what we now call “empty nest syndrome.” She gets inside Betty’s head in a big way. Francine’s orange-y look stands in contrast to Betty’s subdued light-blue dress. Interesting that by the time Betty takes her trip to the farm, she’s wearing an orange dress, albeit not quite as orange-y as Francine’s suit.

After her unsettling coffee date with Francine, Betty comes home, snaps at Loretta and then decides to barrel into Bobby’s school event simply to give herself something to do outside the home (take that Francine!). You can see by Bobby’s pleasant surprise at her offer to help chaperone the field trip – an unusual display of attention from his iceberg mother. Never thought about it before but Bobby has middle-kid-itis.

The awfulness of the field trip experience shows that Betty is as blind to Bobby’s feelings as she has been in the past to Sally’s emotional state. She didn’t go on the field trip for any reason but herself (she certainly didn’t dress for a visit to a farm). The youthful vitality of the bra-chucking teacher sets her off, and then Bobby’s harmless decision to trade away the second sandwich (an indication that Betty remains on the crash-diet track and doesn’t eat much), makes her turn up her portable Guilt Trip Inducer to 11. How could anyone be so blind to their own child’s needs?

Henry Francis, the great enabler, gets it from the look on Bobby’s face. “It was a perfect day and he ruined it.” Who says that over a lost sandwich?? Betty Draper is a character for the ages.

Betty hasn’t changed. Don is trying to change his evil ways — with the wise words of his teenage wild child echoing in his ears from episode 2. Both Betty and Don are having real trouble going with the flow and adapting to the times — as evidenced by how they both dress so squarely by the 1969 standard.

The intricate way these character development moments are woven into the scripts is “Mad Men’s” secret sauce, the killer app, the classic Coke recipe that is often imitated but never duplicated. At the end of an episode this good, right down to the investment in getting the real Jimi Hendrix recording of “If 6 Was 9” “Voodoo Child (Slight Return)” — applause is in order.

Some other observations:

  • Was also waiting for Harry Crane’s entry and he didn’t disappoint. Cocky but not without reason.
  • I am not enough of a film encyclopedia to know what movie Don was watching at the beginning without looking it up online. Nor could I catch what Betty was watching when she was in bed clutching Gene and begging for compliments from Henry.
  • Noticed in that same scene that Betty looks much prettier with her hair down and in a nightgown than she does with her shellacked hair and starchy dress.
  • Noticed that Don was impressed that Megan had met Rod Serling. Guess he really liked “Planet of the Apes.” Serling was a great writer — teleplays for “Twilight Zone” and so many other works so crisp they cut like a knife — and by all accounts a very good person.
  • Jim Cutler is an idiot. Bert Cooper in the final scene pulled the same devilish stare at Don that he did at the end of season 2 when he told Don to just move on from his youthful folly of assuming another man’s identity.
  • I admit, I Googled to see if the Paul Kohner Agency ever repped Sharon Tate. Not that I can tell. Her tenpercenter for most of her short career was Hal Gefsky, who died in 2008 at the age of 90.