WARNING: The following contains major spoilers for the first three episodes of Season 12 of Doctor Who, which airs Sundays on BBC.
In the two-part season opener "Spyfall," Doctor Who pitted Jodie Whittaker's titular hero against her ultimate nemesis, the Master. A Time Lord like the Doctor, the Master is everything she isn't: he has no compassion and he revels in chaos and destruction. Although she managed to thwart his latest scheme to destroy Earth and imprisoned him in another dimension, the Master still, somehow, won.
After going back to her home, Gallifrey, for the first time in a long while, the Doctor discovered that the Master had destroyed the planet. Its cities were left in flaming ruins and the Time Lords were, as far as we know, all killed by the Master. The revelation came as an undeniable shock that rocked the series' status quo -- but it's all part of the overarching mystery of the Timeless Child.
But who, or what, is the Timeless Child?
Shortly after seeing the ruins of Gallifrey, the Doctor receives a message from the Master. He reveals that he was the one who killed the Time Lords after learning the truth about the Timeless Child. Whatever he learned was so terrible and angered him so much that he killed his entire race. In his message he says: "I had to make them pay for what I discovered. They lied to us. The Founding Fathers of Gallifrey... everything we were told was a lie. We are not who we think, you or I. The whole existence of our species built on the lie of the Timeless Child."
Upon hearing mention of the Timeless Child, the Doctor recalls the first time she heard the term. In the Season 11 episode, "The Ghost Monument," the Doctor faced sentient rags called the Remnants, who drew on her history and her deeply buried fears. When the Remnants mentioned the Timeless Child, the Doctor had no idea what they were talking about. "We see what's hidden, even from yourself," they told her, "the outcast, abandoned and unknown."
Then, during the Master's message, the Doctor has a brief vision of the Timeless Child, who appears to be standing at the bottom of a tower overlooking a giant storm that may turn out to be the time stream itself. The Master continues to explain that the notion of the Timeless Child is buried deep in the Time Lords' memories -- and in their very identities.
While there is much yet to be unveiled about the Timeless Child, it appears to be the very basis of the Time Lord race. Whatever the Founding Fathers of Gallifrey did, it would seem they built their entire civilization on a lie.
Did they steal the ability of time travel from this abandoned Child? Or perhaps their ability to regenerate? After all, if the Child is "timeless," then it may have been immortal, and the source of the Time Lords' immortality. Whatever the answer is, it's bound to send major shock waves through the Doctor Who universe.
For the time being, the Timeless Child is the series' latest mystery, and it just might prove to be the biggest in Doctor Who's 56-year history.
Doctor Who stars Jodie Whittaker as the 13th iteration of the titular Time Lord. Whittaker is joined by co-stars Bradley Walsh, Tosin Cole and Mandip Gill in a series spearheaded by showrunner Chris Chibnall. The next episode is set to debut on the BBC on Jan. 19. The new season and all previous 11 seasons will stream on HBO Max later this year.