It's perhaps an appropriate rating in line with the title, but it could've been much more in my opinion. Heatley hits upon a couple of scenes that aren't often (if ever) seen in this type of book. The first one especially, but they feel detached from the more standard side of the story.
Henry is a janitor, who also works as a "cleaner" aka an assassin. His latest job sees him having to kill three people in one night. There's a tight timescale and things are not without their complications.
It's a story that has some original scenes, but they don't mesh with the plot and coalesce to create a satisfying whole.