It's a Past Doctor Adventure featuring Two, Victoria and Jamie in one time-line, and Four, Romana I and K9 (plus Brigadier and Benton) in another, dealing with a weird space-time anomaly which traps the earlier Doctor in a small town based on the Simpsons. I thought there were some good characetr moments - especially for the two Doctors and the female characters - but rather lost track of the plot. Apparently there are lots of Simpsons in-jokes which sailed over my head. Indeed I felt that a lot of the book was the author thinking he was being funny, but it didn't really work for me.
A definite Bechdel pass though. (Having said which, I accept the caveats in this article, pointed out to me by
star_tourmaline, that the technicality of passing the test is not the real point.) Victoria has an off-stage interaction with a female prison guard; and there's a character called Katharine Delbane who meets with the female Prime Minister and is sneered at by Romana. More importantly, it passes the spirit as well as the letter of the test. (Unfortunately, this is not enough to make it a book that I particularly enjoyed.)