The plot is very much a whodunnit (or whodunwhat), and keeps the reader guessing to the end.
The viewpoint of the protagonist, namely "serial killer's girlfriend" is unusual for a police procedural.
I wasn't completely convinced by the characters. At one point I found my self agreeing with the protagonist's mother that she should just get over her trauma. That's not fair of either of us, but I think the failure of empathy is not all mine.
The setting is modern Dublin, which feels a bit like any modern north-western european city: trendy cafes, expensive to live in.