I am currently reading the 43rd book in J.D Robb's gripping In Death series - Apprentice in Death. It amazes me how book after book this series stays strong and fascinating! The case in each book is a standalone but the characters grow from one book to the next to the next and so forth.
The beginning of this book is chilling. It would be at any time, I believe, but with our world the way it is my heart has pounded extra hard more than once while reading this book. If you've never read this series, but wondered about it, I highly recommend it.