In which the trauma of their detention, and Miss Quill's strange reappearance, have caused the group of students to drift apart. The pregnant teacher is hibernating, and Charlie fears what she will be like when she wakes, now that she no longer has the Arn implant preventing her causing harm to him.
Corakinus launches another campaign against Earth - he and his Shadow Kin emerging across the Coal Hill area through various tears in Space / Time.
Amongst his victims are Ram's father, and Tanya's mother. She goes to see Quill to ask for her help, whilst Charlie and Matteusz seek support from Dorothea Ames, threatening her to do so.
When Corakinus goes after Tanya's brothers, Quill steps in and defends them. She then teaches Tanya how to fight back against the Shadow Kin. She must be able to defend herself and her family in the coming conflict.
Following the loss of their respective parents, the distraught Ram and Tanya approach Charlie and demand that he employ the Cabinet of Souls in revenge.
Corakinus threatens Matteusz and attempts to force April to sacrifice herself. Her death will finally free him from being linked to her via their shared heart. He claims he will leave Earth if she agrees, but is lying.
The Shadow Kin invade in force, and Charlie has to finally accept that he must use the Cabinet.
However, Corakinus has linked himself with Charlie as well as April, and both will die if he does so.
The Cabinet wipes out all of the Shadow Kin on Earth, including Corakinus. Quill manages to save Charlie, but April wakes up to find herself in Corakinus' body. As their vanquisher, Charlie is now Shadow King.
Ames passes through a hidden doorway and meets with the Governors. They are unhappy with her handling of the situation, and she is no longer worthy to help them with "the Arrival". She is attacked and killed by a Weeping Angel...
The Lost was written by Patrick Ness, and first broadcast on 3rd December 2016.
It was the final episode of the first series - and would subsequently prove to be the last episode full-stop. The BBC had failed to devote any care and attention to Class, wasting the chance to work meaningfully with a hugely popular author like Ness. The series was shown during a Doctor Who gap year, and it is obvious that Steven Moffat was equally neglectful of the series.
The Lost ends with some loose ends dangling and a cliff-hanger, such as April now trapped in the body of Corakinus, so it is clear that a second series was intended.
Ness later revealed that this would have featured the Governors more, and would have seen a Weeping Angel civil war.
Joining the cast as the Chair of the Governors is Cyril Nri, who had appeared as the enigmatic Shopkeeper in The Sarah Jane Adventures. This makes two Doctor Who spin-off series where he was due to contribute more significantly - only to see it cancelled.
Critics found the Governors to be far more interesting than the Shadow Kin, who were such a generic alien warrior race.
The whole episode was felt to be too rushed, with characters killed off who had never been properly developed in the first place.
Overall, a huge disappointment to what had been a promising series. The final viewing figure for this finale was 0.32 million.