When the writers aim for drama they hit.. damn that was one tense and awesome episode.
In a dedicated Castle board people talked about it being a 3XK episode after the Sneak Peeks came out and more info about the episode.. it certainly fit his style and damn did i yell out when he finally revealed himself (of course we as the viewer and TV show experienced there was no way it was really Castle).
Really set up well and this episode made 3XK even more of a menace than the other episodes.. fortunately Castle is his match and he proved to be pretty ingenious about his escape. It was also "fun" to see Castle be scared for his life.. quite a departure from his usual carefree attitude.
And the way he pulled of a Chuck.. emptying the gun into 3XK's chest was just awesome.. Fillion channeled Malcolm Reynolds pretty well in that scene
Outstanding episode by everyone involved and pretty sure to make quite some Castle episode Top 10 lists.