Kate White's If Looks Could Kill
Bailey Weggins is a freelance writer, mostly for a women's magazine called Gloss. Early one Sunday morning, Cat Jones, the magazine's editor, calls, sounding very upset, and asks her to come over. Since Bailey has known Cat for several years and considers her a friend, she agrees.
It turns out that Cat's nanny is not answering her door, although the lights are on and she is supposed to be at home. Cat convinces Bailey to go into the room, and Bailey finds the nanny's dead body. Saying that Bailey is the only person she can trust, Cat asks her to look into the death, stressing that Bailey, as an investigative reporter, has the skills to do so. Bailey reluctantly agrees, but the more she investigates, the more interested she becomes in the case.
Thanks to Diana Killian for turning me on to this book. It's very well-written, and really hard to put down. Plus, the puzzle is almost impossible to figure out until the last chapter.