Timeless Child

And Tecteum returns in Doctor's time briefly (only in this episode) and unexpectedly: as Division chief she is the person accountable for the appearance of the Flux and for trying (more or less successfully) to destroy the Universe. The moments the two women spend together are at least interesting (and almost shadow the rest of the action): the Timeless Child could have come from another Universe and Tecteum tries to get there after she smashed her original Universe. She has the Doctors memories and it's only a problem of time (almost a week, for us) until she is going to get them back.