At its core, Doctor Who is a show about one person who grows, changes, and evolves over the course of century after century, almost always being with at least one Companion. One could even argue that the Companions are a more important aspect to the show than the Doctor themself. Look at the 4th Doctor travelling with Sarah, vs with Leela or with Romana. In a way, the Companion is what defines the Doctor, and the only thing that gives them meaning in a turbulent universe.

Scherzo pushes this beyond the extreme, into the blatant. Subtext is now text. The themes are the story. The Doctor and the Companion are all there is, and without the Companion there would be no Doctor. Without the Doctor there would be no Companion. Both should reasonably have died, but live only because the other demands it.

In this story, toxic codependency evolves to a toxic coexistence. This brutal, heart-rending story is the deepest and most intense examination of the Doctor-Companion relationship that Doctor Who has ever had or ever will have.