This is the third DS Alex Morrow book, after "Still Midnight" and "The End of the Wasp Season." It really doesn't pay to start with this book, because there's very little in the way of a refresher course for who the characters are. If you don't need to know more than a cursory amount about Alexandra Morrow, then there's no reason not to read this as a standalone. You'll miss what drives Morrow, though.
Denise Mina weaves together three separate stories set in Glasgow, Scotland. Although we occasionally glimpse one from within another, it isn't until the "oh-no-she-di'int" conclusion that we see what they all have in common. The main story concerns a post office robbery and murder of one of the customers who, oddly, seemed to know the masked gunman. The second story is about two bottom-tier police officers who decide to take a bribe from a bottom-tier gangster. Lastly, a politician is in trouble because his indiscretions with women/girls other than his wife seem to finally be about to metaphorically tie his shoelaces together to trip him.
Because there are three stories, it sometimes becomes hard to keep track of where each story was last left. In one case, a criminal is arrested, his real name only mentioned once about 100 pages before, and I had no idea who he was when he showed up again in the story. It's a great fooled-you ending, however, making up for any disjointedness prior to that.
Mina has always succeeded in providing a gritty look at Glasgow, all its warts glowing and growing in economically and morally depressed circumstances. Although the buildup is at times slow, especially in the politician's story, Mina's storytelling ability is powerful and compelling.