A lot of years ago, I was a copywriter at a big ad agency that was famous for hedging its bets. We never went into a meeting with just one idea for a campaign. Hell, we never went into a meeting with just four ideas for a campaign. Better to have twelve ideas; that way, one of them was sure to stick.

One afternoon, we had a pitch for a new account in Chicago. We showed them our first idea, and we wowed them. They were ready to hand us their account. “But wait,” said the president of the agency. “We have a lot more to show you.” By the end of the presentation, we’d showed them so much crap that we talked ourselves out of the account.

So it was amusing to see a variation of this scenario early in ”Mystery Date,” Episode 4 of Season 5 of Mad Men. New copywriter Michael Ginsberg sells Butler Footwear on a new campaign–then keeps talking and ends up selling them on something else. It’s an amateur move, and Don Draper understands that it can backfire. He lets Ginsberg know, in no uncertain terms, that surprises won’t be tolerated.

It should come as no surprise that the air around Sterling Cooper Draper Pryce is still thick with the stench of mortality. But this time, it has nothing to do with getting old; rather, it’s the fear of not getting old that’s infected the world. As if race riots across the nation aren’t threatening enough, eight nurses are found tortured, raped, and murdered in Chicago–and the killer is still on the loose. Peggy’s friend Joyce, who works for Time, stops by the office with grisly photos, which titillate everyone–except Ginsberg, who’s not so self-absorbed he can’t call a sicko a sicko and storms out of the room.

Nowhere is the sense of puritanical voyeurism greater than in the Francis household, where Henry’s mother Pauline is babysitting Sally. Obviously a woman of large appetites, Pauline is gorging on the news from Chicago–and refusing to tell Sally what’s going on. Sally sneaks the newspaper out of the garbage can and scares herself silly. She goes to Pauline for comfort, but, now that Sally knows about the murders, Pauline sees no reason to protect Sally from the truth. Instead, they split a Seconal, and Sally winds up passed out under the sofa.

Which echoes the shot of Don stuffing the body of Andrea, the freelance copywriter he’s murdered, under his own bed. Or–well, let’s take a step back.

The episode opens with Don and Megan riding up to the office in the elevator. Don is sick; he’s hacking, slumping against the back wall. Andrea, a woman from Don’s past, enters and immediately comes on to him. Don introduces his wife; Megan is miffed. Don assures Megan she has nothing to worry about, but Megan is more savvy than that. She knows Don’s proclivities, and treats him with the appropriate amount of wariness.

Don is so sick that, after the pitch to Butler, he goes home. He lies down–but there’s a knock at the door. It’s Andrea–surprise!–who barges into the apartment and thrusts herself at Don. He pushes her out the back door–but, minutes later, she’s back, and she’s in bed with him, and–well, Andrea is persuasive. Later, Don tells her that this sort of tryst can’t happen again, but Andrea promises she’ll be back.

So Don murders her. Grabs her with both hands around her neck and pushes her to the floor and squeezes the life out of her. Kicks her body under the bed and collapses on the bed. It’s truly terrifying moment in which we’re uncertain whether what we’ve just seen is real or imagined.

It is, we find out, imagined, the product of a fever dream. The next morning, Megan is home and the body under the bed has disappeared. How much of Don’s encounter with Andrea was imagined, we have no idea, and neither does he.

Other signs of the times: Joanie’s husband Greg is back from a year in Vietnam. But–surprise!–he’s re-upped for another tour of duty, and Joanie is so distraught that she throws him out of the house. Meanwhile, Peggy–surprise!–finds Don’s new secretary Dawn sleeping in Don’s office. Dawn’s afraid to go home because of the riots in Harlem, so Peggy invites her to spend the night at her place. The two young women find out how much they have in common–and width of the chasm that separates them.

“Mystery Date” is exactly the sort of episode that’s been missing from Mad Men so far this year: a beautiful, self-contained, Cheeveresque short story that stands on its own even while it advances the larger work. The signs of sickness and decadence, the allusions to murder and brutality, are sneaking around the edges of every frame–the butcher knife, the Dick Tracy cartoon voices, the nylon covering Stan the art director’s face. Summer of ’66 is an unsettling time to be alive, and “Mystery Date” captures all the uncertainty with grace and nervous humor, and it's all particularly interesting given the racial tension and fear of violence currently gripping the nation. It’s a nearly flawless hour of television–no need to go on for a minute longer. Some people do know when to quit.