Book characters trying to rescue their writer

I love how this book is told in parallel from the point of view of the writer (Wanda) and her book characters (Trevor and Hannah). Wanda is a girlfriend stuck in a world of submission. In order to survive the relationship, she ends up using drugs and drinking a lot. And that affects what happens with her characters. So they are desperate to help her mood get better so that they can have better outcomes in her writing. And that includes trying to whisper to her in real life that she might need to leave her abusive relationship so things can start to get better. The book is funny and entertaining. It is a quick read as well, with about 240 pages. I read it during a long flight and it was definitely a good way to spend those hours.