I enjoyed the pace of the writing, but the actions of the characters seemed improbable. The author loves to have her characters "liaise", also. They liaise on about a dozen different occasions. To an American reader, that is simply odd. If the word is popular in the UK, I've not heard it used in other books.
Speaking of American readers, just about any of them will be surprised that a university is contemplating shutting down other graduation ceremonies just because one person got shot. Sadly, guns are so common in the U.S., and shootings such a part of daily life, that this "shock" over someone bringing a gun to graduation (our Governor in Texas specifically demands students be allowed to openly carry guns and without a permit, to boot) is also hard to imagine. If only we really did live that way. Similarly, a character being "on drugs" seems dated. Being a drug addict doesn't manifest itself the way it is presented in this book.
As I said, I like the pace of the writing, but I don't believe the writer has an understanding of addiction, drug use, or crime. She is in her most honest voice when she is speaking through the character of the mother. Her other characters do not have the same ring of sincerity.