Caution: spoilers ahead for Doctor Who season 15, episode 3, "The Well."

The big twist of Doctor Who's "The Well" eventually proves to be a secret sequel to "Midnight" from season 4. Taking place many millennia after the Tenth Doctor's visit alongside Donna Noble, "The Well" reunites the Doctor with the faceless menace that tormented him and the other shuttle engers back when the surface of Midnight was covered in diamonds.

Heading into Doctor Who's Pantheon gods, the "Midnight" twist is not easy for those unaware of the online discourse to see coming. Nevertheless, the opening minutes of "The Well" do include a clever clue that gives the twist away for viewers with a good ear for callbacks.

How Doctor Who's "The Well" Gives Away Its Big Twist Early

Did You Notice It?

"The Well" tacitly confirms its connection to "Midnight" only five minutes into the story, before the Doctor and Belinda even enter the mining base. The line in question comes as the Doctor is being introduced to Platoon Leader Shaya Costallion. Shortly after exchanging pleasantries, Shaya explains, "This is Planet 6-7-6-7 and the atmosphere is charged with galvanic radiation." Back in Doctor Who season 4's "Midnight," during the scene where Professor Hobbes was giving his PowerPoint presentation about the planet, he pointed out, "This is Midnight, do you see? Bombarded by the sun. X-tonic rays, raw galvanic radiation."

Professor Hobbes was portrayed by David Troughton, son of the Second Doctor's actor, Patrick Troughton.

"Midnight" is not the only time "galvanic" has been uttered in Doctor Who. The gun used at UNIT headquarters during "The Giggle" is referred to as the "galvanic beam," but "Midnight" remains the most overt instance, and certainly the only time a planet is described as being covered in galvanic radiation. As such, it should have been clear from the very beginning that Planet 6-7-6-7 was merely a cover for Midnight - albeit only if viewers recall a single, throwaway line from almost 20 years ago.

Other Clues Doctor Who's "The Well" Was A Sequel To "Midnight" All Along

There Were Two Other Hints Near The Beginning

While the reference to galvanic radiation is by far the biggest indication that "The Well" is Doctor Who's stealth "Midnight" sequel, other hints are dropped along the way. A little after the six minute mark, Shaya Costallion discusses the carbon 46 being mined on Planet 6-7-6-7. Carbon is, of course, what diamonds are made from, and this is partly how the Fifteenth Doctor himself deduces the truth. By itself, mining carbon would not be enough of a clue for audiences to figure out the big "Midnight" twist, but with galvanic radiation also mentioned within the same 60-second period, it should be clear from the beginning that "The Well" cannot be taking place anywhere except Midnight.

The other breadcrumb is the landscape Fifteen and Belinda look out upon as Shaya Costallion relays this information. At first glance, the craggy and mountainous landscape could be any number of planets from the annals of sci-fi history. Rewatching the "Midnight" scene where the Tenth Doctor opens the screens blocking the shuttle's cockpit, however, the planet's surface seen in "The Well" certainly looks like Midnight without all the shiny parts. Again, it's not enough of a clue by itself to draw a connection between the two Doctor Who episodes, but combined with the other hints, it should have confirmed those suspicions.