The Chronicles of Chrestomanci, Volume One by Diana Wynne Jones. Contains the books Charmed Life and The Lives of Christopher Chant. Recc'd by dropsofviolet, prpl_pen, cumulouscastle, and thisredheadreads.
This volume contains the first two books in the Chrestomanci series, which is set in universe parallel to our own: our world, but with magic. Chrestomanci is one of the world's most powerful magicians, and he enforces the proper use of magic. The first book, Charmed Life, is about young Cat Chant, a boy from a magical family with no magic of his own, who comes to live with Chrestomanci with his powerful and ruthless older sister; The Lives of Christopher Chant is an episode in Chrestomanci's own youth, detailing how he discovered his powers. Cat and Christopher have some similarities in their backstories, so it was interesting to read them back-to-back; at first, I worried that it would be too much like reading the same story twice, but the situations develop differently enough that it turned out not to be a problem.
I have a definite preference for the second book. The first book is enjoyable, the introduction to the world is well done, but Cat is just a little dim for my tastes, and his sister, Gwendolen, is one of the most obnoxious spoiled brats I've ever come across in fiction. I found the young Chrestomanci more engaging and more believable, and the story better written. After Charmed Life, I wasn't certain I was going to continue with the series, but Lives sucked me in and now I'm looking forward to reading more.
I've been meaning to read more Diana Wynne Jones for awhile. Howl's Moving Castle was the first I read, and it didn't do that much for me, but then I picked up The Dark Lord of Derkholm and was thoroughly entranced. So I'm glad I've gotten back to her, and that the experience was so enjoyable.