Harry Potter and the Order of the Phoenix by J.K. Rowling (2003), narrated by Jim Dale
New faces in this book include the aforementioned Dolores Umbridge as well as Tonks and Luna Lovegood. We are also introduced to the Room of Requirement, one of my favorite magical items. Harry is having very strange dreams about visiting the Department of Mysteries at the Ministry of Magic. Meanwhile, he is forced to study Occlumency with Professor Snape, and in the process learns some unsavory things about his father. There were some great subplots, such as Hagrid's trip to see the giants, the story of Neville Longbottom's parents, and Harry's romantic pursuit of Cho Chang. There's a lot in this book and it's all quite wonderful (except for the death of a major character).
The whole thing is oddly relevant to current events: radical groups mobilizing in secret against evil, fake news (that Rita Skeeter!), and a horrible troll wrecking the education system. (Maybe if we're lucky Betsy DeVos will also be carried away by centaurs in the end.) So it was actually great timing that I was listening to this when I was. It was a comfort.
I was quite hesitant to listen to such a long audiobook - indeed, it's more than twice the length of any other book I've listened to. But I never got bored because the story was so action-packed and of course Rowling's style is just so easy to get engrossed in. I've only got two books left in the series, both of which are much shorter, and I'm very much looking forward to finishing the series (again!)