Heartless by Gail Carriger is the fourth of the Parasol Protectorate series. Alexia is back home and due to deliver soon. But there's still BUR matters at hand, including a threat to the Queen that Alexia must investigate.
When Alexia isn't investigating, she and Lord Macon are moving into the home next door Lord Akeldama. Except it's all for show to throw the Hive off Alexia's scent. The supernatural community of London is still convinced that the Macon baby will be a dangerous freak of nature — one worth disposing of.
There's a nice twist near the end, one that I didn't catch because I was too caught up in the antics of very pregnant Alexia trying to keep up with her pre-pregnancy derring-do. Behind all of the old evidence and complex theories, is a simpler explanation.