Season 1, Episode 7: ‘The Legend of Ruby Sunday’

Over six decades, “Doctor Who” has introduced many villains — including big hitters like the Cybermen (first introduced in 1966) and memorable one-off monsters like the gas-mask wearing Empty Child (2005) — as the Doctor’s most fearsome enemy.

But in “The Legend of Ruby Sunday,” the first episode in the season’s two-part finale, it seems his ultimate nemesis might finally have been identified — or rather, rediscovered. It turns out the mysterious villain who’s been pulling the strings this season (“the one who waits”) was first fought by Tom Baker’s Fourth Doctor back in 1975.

This reveal is genuinely fear-inducing. But it’s the combination of Russell T Davies’s pacey, tricksy script and the show’s newly lavish production values that makes Episode 7 such a bone-chilling adventure — one far scarier, far more ambitious, than I expected from the show’s Disney era.

As the finale opens, two mysteries, which Davies has threaded throughout the season, hang in the air. There’s the question of Ruby’s (Millie Gibson) back story, including the identity of her birth mother. And what about the mysterious woman (Susan Twist) who keeps popping up wherever the Doctor (Ncuti Gatwa) and Ruby travel?

These questions are on the Doctor’s mind as the TARDIS crashes into the headquarters of the United Intelligence Taskforce, or UNIT, Britain’s supersecret extraterrestrial task force. He’s greeted by the organization’s head, Kate Lethbridge-Stewart (Jemma Redgrave), and her team, including the 13-year-old scientific prodigy Morris (Lenny Rush).

Right on cue, the mysterious woman’s face flashes onto the screen once more, this time identified as the entrepreneur Susan Triad of Susan Triad Technology. Her name sets off alarm bells for the Doctor. Not only is “S Triad” an anagram of TARDIS (“Obviously, thank you,” Kate says sarcastically,) but Susan is also the name of the First Doctor’s companion and granddaughter.

First, though, the mystery of Ruby’s origins. The Doctor has always said that they can’t go back to Christmas Eve 2004, when Ruby was abandoned, lest the Doctor mess with the timelines. But using surveillance camera footage from that night and a powerful piece of technology called a Time Window, they could recreate that day.

The Doctor and Ruby, accompanied by the UNIT soldier Colonel Chidozie (Tachia Newall), travel back into the shimmering, glitchy past. A hooded woman, presumably Ruby’s mother, appears, but she is even more shadowy than the rest of the picture and Ruby sobs in the Doctor’s arms, unable to see the figure’s face.

Amid the raw human emotion, an existential threat arrives. “What is that?” the young Morris stammers at the Doctor, pointing at a cloud of dust billowing menacingly around the TARDIS.

The readings on Morris’s charts skyrocket. “That thing is hot. It’s cold. It’s radioactive. It’s dead. It’s everything. I don’t know,” he panics. Ruby’s adoptive mom Carla (Michelle Greenidge), instinctively knows its name. “It’s the Beast,” she says, an alien incarnation of Satan himself.

Realizing that Chidozie has gone missing, the Doctor and Ruby call out his name and his distorted voice responds in a low, inhuman growl: “I am in hell.” In the Time Window, the system overloads and the Doctor and Ruby are ripped out of the memory. Chidozie’s corpse returns with them, turned to dust.

Unnerved, the Doctor demands that his former companion Mel (Bonnie Langford) take him to Susan, who is about to give an important speech at the United Nations in her role as chief executive of a giant tech firm. If the Doctor is her grandfather, she doesn’t recognize him, greeting him pleasantly: “Nice to meet you, pet. Doctor, who?” providing a brief moment of levity.

Susan tells the Doctor she’s been having “lot of dreams” and the Doctor asks what she dreams about. Is it Lindy, the spoiled influencer from the episode “Dot and Bubble”; or the deserted planet from “Boom”? Her look of shocked recognition confirms that somehow, Susan is part of this.

At the UNIT headquarters, the TARDIS lets out a baleful groan. UNIT’s members look terrified once more; nobody does wide-eyed terror quite like Redgrave. Morris confirms that this isn’t just happening in the past, and the enemy has woven itself into the Doctor’s ship.

A feeling of dread pervades Susan begins her speech. She awkwardly dances onto screen with a stiffness instantly reminiscent of the awkward boogie by Theresa May when she was Britain’s prime minister. . But as Susan prepares to read the words “I think we can succeed” on the teleprompter, that same sinister, echoing, demonic voice says them first.

At UNIT, the previously perky staffer Harriet (Genesis Lynea) starts speaking like a woman possessed about “the king himself.”

“He has hidden in the howling void,” she chants. “The Lord of Time was blind and vain and knew nothing.” Her name, it is revealed, is Harriet Arbinger, another wordplay on “harbinger,” just like Henry Arbinger in “The Devil’s Chord.”

“The gods bring harbingers to warn us of their coming,” the Doctor whispers. But which god, he ponders, and Harriet lists gods of chaos from past “Doctor Who” escapades: Neil Patrick Harris and Jinkx Monsoon’s father-child duo of Toymaker and Maestro; the Mara, a snakelike creature faced by Peter Davison’s Fifth Doctor; and the Trickster from the children’s spinoff show “The Sarah Jane Adventures.”

With every god, and the terror they brought, tension builds. By the time Harriet warns that “standing on high is the mother and father and other of them all,” the anticipation feels almost as unbearable for the viewer as it seems for the characters. “Whatever it is, here it comes,” Kate says.

The “god of all gods” at the heart of this story, Harriet explains, has “one true name” and it is revealed as Sutekh.

For the first time this episode, all sound recedes, save for the Doctor’s sharp, shallow panting. To newer “Who” fans, the name might not mean much, but erstwhile viewers may remember Sutekh from the 1975 episode “Pyramids of Mars.” Inspired by the Egyptian god of violence and storms, he is the “god of death,” hell bent on destroying all life in the universe.

Before the TARDIS, the dust cloud coalesces into a monstrous, dog-like beast with multiple red eyes and sharp fangs. Susan’s head cracks back and her face becomes a skeletal horror, with red glowing eyes peering from sunken sockets.

“Did you think I was family?” this new, horrifying Susan asks the Doctor. Her hand reaches out to pulverize the Doctor, who is terrified.

“I bring Sutekh’s gift of death for you, and for all your tiny, vile, incessant universe,” she says, the episode ending on this cliffhanger. Has the Whoniverse ever been this scary?