I've recently become hooked on all the Peter James books, particularly his Roy Grace detective series.
His books are easy to read and keep your guessing right to the end. They can be a touch graphic and gory, but that makes them all the more enjoyable in my opinion.
I've read all 6 previous books back to back as I can't get enough of them, and while it helps to read them in order to follow the main characters that flow through every book, each book stands up on it's own and can be read without having to have read the previous ones.
If you see any of these in a charity shop, you won't regret picking them up.