After the events of last week’s episode, which left the Doctor blind, he now has a compelling reason to use the Sonic Sunglasses. He is able to create a flawed facsimile of sight by using the sunglasses to scan his surroundings and transmit telepathically to his mind. The episode is kicked off by him receiving a message on the glasses from himself—or rather, a digital version of him in a computer simulation.
After being recruited by the Vatican, the Doctor must figure out the mystery behind an ancient text known as Veritas. Whoever reads it inexplicably kills themselves. The episode is set inside a digital world where the people are unaware they are part of a computer program, and Veritas informs the reader of this. The purpose of this simulation is to prepare invaders to conquer Earth. My big problem with this episode is that if aliens planned to take over Earth and built a computer program to test plans of attack, then why would they add Veritas to the program? If you want untampered test subjects, then do not tell them they are test subjects.
Also in this episode were flashbacks to Missy’s execution. It is possible that her captors were the Time Agency, as they appeared to have vortex manipulators similar to Jack Harkness; however, not much is said about them. These scenes were interesting and we finally got the explanation that she is what the Doctor is guarding inside the vault, but I wish they had been in another episode (or spread across several episodes). This was already a complicated episode, and adding the flashbacks made the story even more convoluted.