That's one small two-step for SC&P, and one giant leap for Don's humility.

So, who was expecting that? Not the death. I was suspecting someone would be killed off with Ted’s death wish and the looming Mets pennant. And not Roger swooping in to save Don and the agency. We’ve been rooting for an underdog all season — we just didn’t know it was Roger. And not Sally’s amped up cynicism and sass, either. That’s just business as usual.

I mean Bert’s dance from beyond the grave.

Say what you will about the episode’s ending — bizarre and out of place, or comical and uplifting (Twitter seemed pretty evenly divided) — but if there’s one thing "Mad Men" never fails to deliver, it’s a shocking season finale. Kudos, because a musical number by Bert Cooper was the last thing I thought I’d ever see.

Not to deny Robert Morses’ singing and dancing talents. He did portray J. Pierrepont Finch in the original Broadway and film production of “How to Succeed in Business Without Really Trying."

But a full on song-and-dance routine? With an on-the-nose tune about the “moon [belonging] to everyone” after devoting a good chunk of the plot to the moon landing? Forget the sentimental and heartfelt waltz Don and Peggy had last week. This is flat out cheesy.

Stop clutching your playbills in dismay. I’m not one of those musical haters. I love musicals. I even watched Ken’s drug-fueled, cane-twirling time step on loop last year.

But there’s a time and a place for people randomly bursting into well-choreographed show tunes. “Mad Men” is not one of them. And, no, “Zou Bisou” doesn’t count.

What’s frustrating as a “Mad Men” fan is that I enjoyed this episode wholeheartedly — Peggy triumphed, Roger triumphed, America triumphed, hooray! — except for those last few minutes where it jeté-d into “Glee” land. It soured the entire episode.

How can a show so hell-bent on making its fans uncomfortable with tear-jerking suicides and gag-inducing nipple lacerations end its midseason finale on an upbeat musical number? And how does this exactly entice me to watch the rest of the final season (back next year!)?

Enough griping. The show must go on. Let’s try to dissect this symbolism behind this song. (There must be some reason it’s there, after all).

Show creator Matthew Weiner has previously said that this season was meant to explore the “material world and the immaterial world.”

The Broadway-inspired hallucination promises Don, “The best things in life are free.” Next season could be the start of Don’s departure from the money — and material — obsessed life of Madison Avenue.

Like Ted, he might seek the meaning of life beyond the business meetings — without turning to the bottle or turning off the airplane engines. It’s not a far stretch. McCann & Erickson and GM think that Ted and Don are “one person.”

This season, however, seemed more focused on the perils of the future. The marvels of technological achievement are claiming its victims. First Ginsberg went over the edge with the arrival of the computer; now Burt died right after the moon landing.

Roger knows his demise is imminent, along with everyone else’s at SC&P. “Cutler’s not going to stop until the firm’s just Harry and the computer,” he warns Don.

That means Joan, the mother of Roger’s child, and Peggy, Don’s protégé and eventual successor, will be out. Suddenly, the two most selfish SC&P employees (and that’s saying a lot) put their team first, not themselves. They become leaders.

“No man has ever come back from leave, not even Napoleon.” Bert doesn’t know Don as well as he thinks he does. Don’s error in the past was his pride. Always impulsive, never selfless.

This shift in Don’s ego didn’t happen at the drop of his feather-trimmed hat. Mentoring Peggy and cheering her on has made Don realize that not everything is about him.

Without his pride getting in the way, joining forces with McCann & Erickson was an easy decision. It’s what he needs to do to keep his job and everyone else’s. It’s not entirely selfless, but it’s a start.