I was reading these between manga series, and I have to say I was underwhelmed. This isn't the Garth Nix of Sabriel, Lyriel, and Abhorsen ... we're back to the Garth Nix of >sigh< The Ragwitch.
Asthmatic Arthur Penhaligon is a young teenager in what seems to be a near-future Britain, which is a more totalitiarian place than it is today. He's destined to die because of complications from his illness, but instead becomes involved with a mysterious artifact that turns out to be a Key. He has, in fact, become part of a Collect-the-Coupons quest, to use the terminology of Nick Lowe's essay in Ansible.
( Read on ... with spoilers and some snarkiness ... )