Agreed. This episode was awesome. I am very curious to find out what this Linchpin is. Plus i never expected that Castle and Beckett would someday save the world as we know it, but it looks like that is the case in this episode and the next one.
I did however expected the ending, where the professor was about to tell everything and than something distracts him and he gets killed. I must have seen that scene at least a hundred other times in different tv shows and movies.
I wonder if this will all somehow connect to Beckett her own case involving her mothers death. That would be so cool!