Doctor Who is back for a brand-new season, along with the Fifteenth Doctor (Ncuti Gatwa) and his companion, Ruby Sunday (Millie Gibson). With the arrival of Doctor Who'sfourteenth season on Disney+, the long-running sci-fi series is welcoming a new generation of fans to join a veritable legion of experienced Whovians.

Whether you've been a fan of the Doctor since the initial run, fell in with its 2005 revival, or have just started wading into all things "timey-wimey," returning showrunner and writer Russell T Davies is offering treasures with the premiere episode "Space Babies."

Along with a space-set fairy tale of monsters and derring-do, "Space Babies" delivers a bumper crop of references, questions answered, and other assorted Easter eggs. Here's what you might have missed.

Gallifrey is gone, babes.

Gallifrey, home of the Time Lords, has spent the last 20 years bouncing in and out of existence on Doctor Who. In Davies' first era as showrunner (2005-2010), the planet had been wiped out in a mysterious Time War with the Doctor's main enemy, the Daleks. Wiped out, we were led to believe over seven seasons, by the Doctor himself.

That all led up to the Doctor Who 50th anniversary, in which the loss of Gallifrey was expertly retconned by then-showrunner Steven Moffat. The Doctor made his way back home over two seasons as Peter Capaldi's Twelfth Doctor, finally sending big bad president Rassilon packing in "Hell Bent" (Season 9, episode 12)."

Then, in Jodie Whittaker's Thirteenth Doctor era, controversial showrunner Chris Chibnall told us Gallifrey had been destroyed again. This time, it was because the Doctor's ultimate frenemy, the Master, found out that all Time Lords including himself had the Doctor's DNA in them as part of the so-called Timeless Child reveal and... had a fit of rage sufficient to destroy an entire people in some way? It was never quite clear.

Now with "Space Babies," Davies confirms that the Doctor's world of Gallifrey is "gone." Gatwa's Fifteenth Doctor says it twice, in two registers, in one of the episode's most affecting line readings. The Doctor's recurring search for home is no more. As in Davies' first tenure, the lead character is the last of the Time Lords.

What Davies appears to be signaling is that he's not going to retcon Gallifrey back again; the Chibnall genocide (which is here explicitly called a genocide for the first time) was for real. And really, in story terms, the call is a no-brainer. The Doctor is better off without those pompous big-collared elites cramping his new sense of style.

"Space Babies" tackles the butterfly effect. (No, not thatbutterfly effect.)

At the start of "Space Babies," Ruby Sunday gets firsthand experience on how a little change in the past can radically alter the future. When visiting the dinosaurs of long ago, she accidentally crushes a butterfly — and just like that becomes an ornery reptilian hatchling. (Good thing the Doctor's quick thinking resuscitates the fallen bug and sets things right!)

Beyond setting up some basic rules of time travel in Doctor Who, this simple scene of Ruby stepping on a butterfly has an older lineage than you might think — even older than Doctor Whoitself.

The 1952 Ray Bradbury story "A Sound of Thunder" features a time-travel safari skipping back 65 million years in order to hunt for T. rex. The hunters are constantly told not to change anything in the past lest they change their present, and they think they've heeded the warnings — until one discovers a dead butterfly on the sole of his shoe. That changes something crucial in their own time: a fascist candidate for president, who'd lost when they left, now appears to have won.

That's the don't-step-on-a-butterfly rule of time travel reflected in Doctor Who,which is not to be confused with "the butterfly effect," which boils down to the "butterfly flaps its wings and causes a hurricane around the world." Though the two are often conflated, the latter has more to do with chaotic patterns resulting from tiny changes in large systems like, say, the global weather, than it does with the theoretical realm of time travel.

Whatever you call it, Doctor Who has had some fun with the "don't step on a butterfly" rule over the years. "Tell you what then, don't step on any butterflies," David Tennant's Tenth Doctor tells Martha (Freema Agyeman) when she brings it up in "The Shakespeare Code" (Season 3, episode 2). "What have butterflies ever done to you?"

The butterfly chat goes in a different direction when Bill Potts (Pearl Mackie) brings it up to the Twelfth Doctor in "Thin Ice" (Season 10, episode 3). "I mean, that's what happened to Pete," the Doctor says, deadpan, making up a companion on the spot. "He was standing there a moment ago, but he stepped on a butterfly, and now you don't even remember him."

But when Ruby actually steps on a butterfly, it marks the first time the Doctor has seen the result in person — what he deserves for teasing Bill, perhaps. Luckily, he was able to revive the butterfly, but how? Regeneration energy? Can the Doctor bring creatures back to life now? It isn't clear.

RememberWALL-E?Meet Nan-E.

If you saw the self-driving baby carriers in "Space Babies" and thought of the baby-like, helpless humans revealed to be in a space station at the end of the beloved Pixar movie, you're not the only one.

The homage is clear. And it becomes even clearer when we learn of the existence of Nan-E (Bridgerton's Golda Rosheuvel), a robotic voice with an anti-swearing filter, chosen as a pun on the traditional British "nanny." But this one turns out to be an isolated carer who's a bit more homicidal (or strictly speaking... booger-cidal?) than WALL-E the robot ever was.

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The Bogeyman enters.

In the Peter Capaldi episode "Sleep No More" (Season 9, episode 9), the Doctor encounters a monster that is literally made out of sleep. Not the act of losing consciousness, but the stuff that gets in your eyes overnight, aka eye boogers.

Some fans thought that choice was the bottom of the barrel when it comes to Doctor Who monsters. But apparently there's a whole other barrel below it, and it contains nose mucus. Welcome to Doctor Who canon, bogeyman! (A TARDIS-style translation note: Bogeys in the UK are boogers in the U.S., and the UK bogeyman is the same as the U.S. boogeyman.)

Davies has all the juvenile linguistic fun you might expect, including Ruby's expression of disbelief: "It's not." It is, of course, snot.

Appropriately enough for this episode, the old English name of the mythical creature used to scare children since time immemorial simply means "frightening specter."

What is the Doctor's real name?

An oldie but a goodie in Doctor Whois totease the notion that the Doctor is about to reveal his actual secret Gallifreyan name. And no, his actual name is not "Who." Although former showrunner Steven Moffat likes to point out there are plenty of indicators throughout the classic series (1963-1989) and the revived series (since 2005) that the full title of the show is what the universe actually calls him.

Moffat's episode "The Name of the Doctor" (Season 7, episode 13) is the ultimate tease. Even with a title like that, it fails to reveal any name beyond the Doctor."The name you choose, it's a promise," Matt Smith's Eleventh Doctor insists, and that's been good enough for fans ever since.

That doesn't mean Davies won't continue to tease it, as he does at the end of "Space Babies." In the premiere ep, he's about to tell Ruby Sunday and her family his real name as he closes the door of the TARDIS. But as in "The Name of the Doctor," our attention is distracted by something else. In this case, it's a TARDIS scan revealing that whatever Ruby Sunday is, she is actually human (and thus not a Time Lord.)

Doctor Whostreams Friday, May 10 at 7:00 p.m. ET on Disney+, where available, and simultaneously on May 11 at midnight on BBC iPlayer in the UK.