Love the graphic. Very 60s/deco-ish, clean lines, simple but strong elements that convey theme well. Top-weighted, which gives it an uneasy feel, as if it might come crashing down -- fits with the plot.
Nice placement of the 'eye' graphic, in the lower right third, a little too close to the right edge -- as if you're being watched by someone off to the side rather that looking at something meant to be on display. This element is also a tad too far from the bottom which enhances the threat from the unknown entity who watches, looking down on you from a position of power when you (the one who observes the poster) should be looking down on it.
I like how the main 'splatter' element dominates the center, asserting itself, lending more weight to grisly facets of the story. The point of the 'knife/eye' penetrates deep, almost all the way, nearly to the other side, driving the point home, as it were.
The placement of the 'eye' in the knife blade conveys what I'm guessing is a central theme of McGowan's novel: Lost kids sometimes turn to violence to create a sense of identity and, as such, their weapon(s) become intimately associated with who they are. So: "I am this knife. Without it I'm nothing."
More posters should be like this.