Extremis (Doctor Who)

Extremis is the sixth episode of the tenth series of the British science fiction television programme Doctor Who. Written by Steven Moffat, it was first broadcast on BBC One on 27 May 2017.

The episode revolves around a virtual reality simulation created by the Monks, a race of aliens planning to invade Earth. They developed the perfect simulation, housed in a massive virtual reality chamber known as the Pyramid, to observe and learn about Earth's governments and their potential defenses, allowing them to devise the most effective strategy for conquest.

In the episode, the Doctor, who is temporarily blind due to a previous encounter, investigates a vault under the Vatican that holds a mysterious book called the Veritas. The Veritas contains a suicide message, a warning about the simulated reality the Monks are creating. Simultaneously, the Pope calls upon the world's major governments to cooperate in the face of an impending, unknown threat.

The Doctor, Nardole, and Bill Potts discover that they are within the Extremis simulation. Crucially, the Doctor, despite being a simulated version of himself, realizes the truth. Before the simulation collapses, he manages to email the information he has gathered about the Monks' plan to his real self, using the simulated reality's inherent connection to the real world to transmit data.

The word "Extremis" in this context refers to the extreme measures taken by the Monks and the perilous situation facing Earth, as well as the desperate act of the simulated Doctor in sending information to his real counterpart. It highlights the potential for annihilation that exists if the Monks' invasion plan succeeds. The episode also touches upon themes of faith, truth, and the nature of reality versus simulation. The cliffhanger ending shows the Doctor reading the email, revealing that he now possesses knowledge gained from a simulation.