It's a simple horror story at first. At seven past midnight a monster comes to Conor's bedroom window and asks him if he's afraid. The trick is that Conor isn't afraid of the monster, because he's already seen something much worse in his nightmares. But the monster will make him face his fear by telling him three stories and then making him tell his own. The truth.
What can I say about this novel other than it's a short and gripping tale that haunts you even when you're finished. It's not the horror of Goosebumps or old monsters like Frakenstein and Dracula, it's the fear inside yourself, of frailty and helplessness but articulated in such a dark and terrible way that we, like Conor, almost dread the truth of it coming to light.
Ness doesn't use extraneous words. This is more of a novella than novel, but each story the monster tells conveys multiple messages as it draws parallels to the difficulties in Conor's own life and never gives him a direct answer. The true weight of the tale isn't in the supernatural but how Conor is affected by the grief he feels at his mother's cancer, the resentment he has toward his father and grandmother, the resignation he has to the bullies. There is never an attempt to glorify or prettify the process, and the lyrical nature of his prose is tied into how brutally this story affects Conor.
The illustrations by Jim Kay are at times stark and other times detailed and beautiful. They are a perfect accompaniment to the story, and I feel it would not be told as well without them. Normally the trick of making people afraid is never to directly show what it is we should be afraid of, but Kay's portraits are an imprecise focus as much as the monster's stories are. And they are applied expertly along the margins and between the pauses of the story's breath. And one portrait of the great monster sitting down in almost resignation can be moving in how the dark feelings mirror each one.
This is a story about confronting the inescapable and dealing with the inconsolable, and it is done in a way that never makes the real feelings take a backseat to the fantastic. Other stories have handled the same conflict in a similar supernatural fashion, particularly the graphic novel "I Kill Giants" by Joe Kelly and J.M. Ken Niimura. And while that story is good, "A Monster Calls" is perfect in conveying the twisted up emotions of the grieving process.