well that wasn't a surprise the book i mean, if memory serves me right in i forget which season he talked about getting that book by a stranger when he was 10. but that stranger being his father that part i liked. also if you recall Alexis asking him about his dad he i believe said he used to pretend him being a spy i think.i may be wrong on that part granted cause it's been awhile since i last watched it but i think that part may be right. and when it was implied last season that his dad is the one who got him in the CIA but from the one who told him that it was really hard to believe if she was telling the truth or not. so that being the truth i kinda like.
though i DO wish that the end of the episode with him starting to tell Martha wasn't cut off. i would have loved to have seen both their reactions her and beckett's. it was kinda of a let down in a way and only cause i would have LOVED to see Castle go the "Taken' route where he really didn't need to kill anyone if the writers didn't want him to but to just have him throw that one aside was the let down. great episode overall and these 2 are prolly my favorite this season so far.