"The Auntie Matter" is another Big Finish audio drama. The 2013 production is about 60 minutes long, in two parts.
Trouble seems to find the Doctor - especially the Fourth Doctor - even when he isn't looking for it. Even when he is especially keen to avoid the attention of the Black Guardian...
Taking place just after the Key to Time stories (Season 16 of the classic series), before Romana regenerates, the Doctor (Tom Baker) and Romana (Mary Tamm) are lying low in a London Town house in the 1920s, Lord and Lady of the house. The Doctor has left K-9 aboard the TARDIS and set the ship to visit a thousand random locations before returning to Earth in order to keep the Black Guardian, presumably still displeased with the Time Lord and Time Lady after failing to gain the Key to Time, from finding them.
Elsewhere, Reginald brings his fiancee to meet his "aunt" - whereupon the "aunt" takes over the young lady's body. Reginald's memories of the event are erased and he is sent out to find an attractive, smart, young lady to marry.
Reginald encounters Romana and takes a fancy to her. He feigns interest in science to attract her attention, and she travels with him to Bassett Hall to meet "Auntie." Meanwhile, the Doctor goes off with Mabel, his maid, in search of an alien energy source he detected. It's no surprise that the source is Bassett Hall.
Tom Baker and Mary Tamm are terrific (and, with an audio production, I can still visualize them as they looked in 1979. The story has a great deal of humor in it (just like a Tom Baker story from the classic series, come to think of it). Add some killer androids, mix, and one has a great story.