Okay, this book is too good to spoil. So I won't. I'll just tell you you have to read it. It gave me nightmares the first night after starting it, nightmares bad enough that I almost texted my best friend to tell her that if a certain thing happened to me, to blame the villain of this book. It made me paranoid. If that's not a positive review, I don't know what is. So, go out and read this, and completely ignore anything under the cut until you're done. Trust me, it won't take long.
A man awakes on the floor, and realizes he remembers nothing at all about his life. He's lost every personal memory he has. He finds out that this is the eleventh time this has happened to him, and that each time, he's lost another bit of himself, until he's reached this point of blankness. Soon, he starts getting letters from himself, prior to the memory loss. They describe what's happened to him, at least what his previous self can remember. He's the victim of a Ludovician, a conceptual fish that feeds on memory and self, and worse, one that's decided that one bite isn't enough, that wants to consume all of him until he's nothing but a shell. He goes on a quest to find out the whole truth, how the Ludovician found him, and seeking a way to stop it.
And as I said, it's fucking amazing. I'm definitely a fan of world building, and not only does Hall build a world in un-space, he also builds an entire ecology of animals that are purely conceptual. He practically makes a field guide for them, for identifying them and defending oneself against them. And the concepts freaked me out like House of Leaves, and the adventure thrilled me like Neverwhere.
And the wonderful thing is, he doesn't skip on the writing or characterization. All of them are fully realized, people that have personalities, and drives, people you can identify with. There are scenes which you can picture in their entirety. I just loved this one.