Spoiler warning: Do not read on unless you’ve seen episode 4 of “American Horror Story: Hotel,” titled “Devil’s Night.”

“American Horror Story” revels in its Halloween episodes; after all, it is a horror show in prime October scheduling. And while episode four of “Hotel,” “Devil’s Night,” was a bit shorter than the previous episodes this season, it brought out some very devious special guests.

Some of America’s biggest serial killers — Aileen Wuornos, John Wayne Gacy, Jeffrey Dahmer — made appearances at the Hotel Cortez. The most unexpected turn, though, seemed to be the apparent takedown of the country’s fascination with the murderers near the end, as James March (Evan Peters) praised them for living his “American Dream.”

But first thing’s first: Holden is home. Alex Lowe (Chloe Sevigny) finally got her wish and her beloved son is returned to her after she found him at the Hotel Cortez. But Scarlett’s observation from the last episode, that he doesn’t feel “normal emotions,” seems chillingly accurate. Holden isn’t happy or sad that he’s been taken home — instead he’s emotionless, and only wanting his “other mommy,” the Countess (Lady Gaga).

Alex gets the full picture when she finds him feasting on the family dog, which prompts her to head straight back to the hotel.

Meanwhile, John Lowe (Wes Bentley) finds out he has a lot more in common with the hotel maid, Miss Evers (Mare Winningham), than he ever could have expected. She tells him about how her son was abducted on Halloween while he was in full ghost costume — not unlike how John lost Holden at a busy fair. Miss Evers would later find out that her son was killed in a mass child murder.

Her story answers a lot of questions about the character, namely why she’s so obsessed with keeping the hotel’s sheets white. The image of her son, last seen draped in a sheet, is heartbreaking. Though the real question is, if her son was murdered by serial killers, why is she so loyal to March?

When Alex gets to Hotel Cortez, she finally collides with the Countess, who doesn’t withhold information from her. On the contrary, she answers all of her questions, revealing that she was the one who took Holden. She says Holden “contracted” the ancient blood virus that made him a shell of who he was — a curious way to describe it, given that the disease isn’t passive, but is inflicted on someone by the Countess.

She apparently kidnapped Holden because “the world can be such a dangerous place,” though does the Countess really act outside of her own interests? She also manages to drop one of the coldest lines in the show thus far.

“I’ve never neglected my son,” protests Alex.

“You say the same about your husband,” the Countess responds, likely digging a deep cut into Alex. The Countess offers to give Alex the ancient blood virus, getting her son back for all of eternity, in exchange for Alex’s undying loyalty. It’s an offer that, we later learn, Alex, for all her threats to the Countess, couldn’t turn down.

The biggest event of the night, though, is the Devil’s Night dinner. As Liz Taylor (Denis O’Hare) explains, it’s an annual feast that tops Halloween, as it’s when the “real ghouls” come out to play. It brings America’s deadliest serial killers into town for one night, the first of whom we meet is Aileen Wournos.

“AHS” veteran Lily Rabe makes her debut in the episode as Wournos, a woman who killed seven men in Florida between 1989 and 1990. Rabe embraces the challenge with pure, unhinged insanity pouring out of her performance as she seduces a drunken John, who’s now apparently back to drinking after swearing off booze.

John thinks it’s a Halloween costume, but he’ll learn that he’s sorely mistaken. “You try to take something from Aileen Wuornos, and I swear to Jesus H. Christ, I will take everything from you,” she tells him.

They head back into a room, where Aileen proceeds to make things very uncomfortable. John narrowly escapes her, avoiding what would have likely been a murder.

But it’s not the last he’ll see of her. John, for likely no reason other than to get some answers, suits up and attends March’s dinner, where we’re introduced to the serial killers. Along with March and Wournos sits Gacy (“Freak Show’s” terrifying John Carroll Lynch), Dahmer (Seth Gabel), Richard Ramirez (Anthony Ruiviviar) and the Zodiac killer.

Why John was invited to this assortment of cold-blooded killers is initially unknown. Is there something horrible that we don’t know about John? For his part, the detective deduces who they are, but points out that they’ve all died.  Don’t worry: when he tries to shoot Dahmer, they inform him of the obvious: that they are indeed dead.

March, for his part, is a perfectly accommodating host. When Dahmer rejects a salad (Wournos makes a joke about him preferring red meat), March brings out a human victim, ready for Dahmer to feast on. That’s hardly even the most disturbing part of the meal.

For “dessert,” Sally brings in a man she found on the street and drugged, in exchange for being left alone for a year (and for someone who has preached compassion, she clearly only looks out for herself). March is disappointed that John’s not “one of them” yet, and it’s curious that March sees some kind of potential in him.

March gives an impassioned speech to the killers about how successful they are, pointing out that they’ve had books written about them and movies based on them. “Johnny Depp likes my paintings,” says Gacy with glee. Is “AHS” — a show which has featured serial killers prominently — taking down the media’s fascination with them?

After John watches them kill the innocent man together, he blacks out and wakes up, disoriented. Sally tries to tell him that it was all just a dream, or that he was hallucinating. The killers, however, are just in the other room.

It looks like John will either have to become one of them, or be killed by them.

As for Alex, she takes the “become one of them” approach, drinking the Countess’ blood to become one of her immortal creations.

This adds one to the team of the Countess, who may need it, as it looks like she has some sizable competition coming her way in the form of Ramona (Angela Bassett).