First thing: I don't buy the storyline at all. The premise: the murderers of Kate Becket's mother are so powerfull and well connected -- they can kill her without any doubt and remain hidden. A gang of renegade cops, who made millions of dollars in the 70's by kidnapping mobsters is behind this. And Montgomery has to sacrifice his life to keep Beckett alive. This does not make any sense at all.
The real reason behind this plot. Castle and Becket have to keep up their sexual tension. Since they are bot smart, attractive and very attracted to each other, the writers need better reasons. They coupled both up, but now they have to resort to deep emotional injuries to keep them apart -- and still together. On their way through a New York that is worthy of any mystery novel.
All this is very transparent. But I still like this episode inspite of the lack of surprises. The ER scene is masterfully directed. The writers did a good job to keep the story on running and to show the successless hunt for clues. Fillion and Katicstruggle with the emotional state of their characters, but they do a great job.
Especially I enjoyed to see two actors from Star Trek. Michael Dorn als therapist is a bold casting decision :-)