I enjoy writers who can hook your interest on the first page, and keep your interest right up to a cliff-hanger ending. I've read nearly all of the Rebus books by this author-enjoying them immensely, but Witch Hunt is even better than the dour Scotsman.
This book has all the elements-people from the old school of spying, to the new electronics whiz kid, with a smattering of re-kindled middle age romance to young international romance; and loads of suspense.
This story is about the search for a chameleon like paid assassin and her unidentified UK target. A number of agents from MI5, it's French counterpart, and Special Branch, must fight to overcome interservice rivalries in order to stop the assassin, without much time to do it. You won't be able to put the book down until the end.