HaBO: Spy vs. Reporter Aristocrat

You did it! We figured this one out! It is a truth universally acknowledged (by me for certain) that the Bitchery pretty much knows everything, and really, it's true. Scroll down to see the solution for this HaBO - and many thanks!

Usually the HaBOs are looking for older books. This one is recent. Angela writes:

I was wondering if you could post this in help a bitch out. It isn’t a book I read, it’s a review of a book that I read. Of course now that I want to look the book up and actually read it, I can’t remember the title or even where I read the review.

All I remember about it is as follows:

1. It is set in the 1930’s or 40’s

2. The heroine is both an aristocrat and a reporter.

3. She goes to a house party and her brother’s friend is there.

4. The purpose of the house party is for everyone to indulge in sex games.

5. She and the friend, who is a spy, pair off.

6. There’s a mystery or a spy thing involved.

6. It may be first person narration.

I also think it is fairly recent but that could be just because I read the review recently (last 6-9 months?) Anyhow, it is driving me batty and I hope that someone out there will have the answer.

Sounds like something steamy-  anyone recognize that book?