The Assassin is a direct follow up to Stephen Coonts last Grafton & Carmellini adventure, Traitor. It brings to a conclusion the pursuit of master terrorist Abu Quasim that began during Traitor, so if you haven't yet read that novel I would recommend doing so before starting The Assassin. Traitor is somewhat implausible, but still an above avergae thriller.
The Assassin is a great improvement on the book that precedes it. Whereas Traitor relied on an implausible central plot device that never rang true, events in this lastest Coonts thriller feel far more believable.
Once again Grafton and Carmellini make a fine double act, with Carmellini doing the physical action man stuff with aplomb whilst Grafton is the inscrutable brains of the operation. The rest of the cast of characters are reasonably well drawn, although none make it much beyond being one or two dimensional plot devices.
The plot itself is pretty convoluted and takes a long time to reach what end up being two separate finales, if that isn't an oxymoron, one immediately after the other. Its holds your attention whilst it gets there, but you don't want to think too hard about it or you'll be spotting more plot holes than the story could be expected to survive. Some of the story elements also feel a little dated, drawing as they do on real life events from a number of years ago, but not to the extent of ruining the book.
Surprisingly The Assassin is also pretty brutal in places. I never had Coonts down as that sort of writer, but the body count here is pretty high, with the good guys coming off almost as badly as their enemies and often in pretty bloody, painful ways. If you're at all squeamish about such things this side to the book might put you off.
Overall however, The Assassin shows that Stephen Coonts can still produce solid, entertaining thrillers that easily compete with the best in the genre. That's not bad for an author who has been around for so long and to my mind remains underrated. The Assassin isn't going to go down as a classic, but its still a damn sight better than some of the later, lazier and tired efforts put out by other authors who have been labouring in the thriller genre for similar lengths of time.