Although Ghost light was the second story of season twenty six, it was the last to be produced.
It is a macabre tale of an alien presence trying to control evolution set within a Victorian house.
It is the ongoing theme of the Doctor challenging and tutoring Ace continues in this story. Here he is testing her initiative by, unknown known to her at first, bring her to the very Victorian house that she blew up aged 13.
Costume dramas is a genre which the BBC has always excelled at. Though during the late 1980's they had stopped producing them. So maybe that's why the sets look so good in this story. It's clear to set the amount of love that went into producing them.