I loved that they let Castle go so dark in the search for his daughter that he "reasoned" the farmhouse location from the driver. And the exchange between Castle and Beckett where she said she didn't know he had that side to him...
I also loved how the usual hard Gates gave her people the "all clear" to do whatever they had to do to get Alexis back to Castle. For all the guff she gives him, she still sees him as "part of the family".
It will be interesting if these events have any lasting effects on them. Castle going as far as he did, Beckett letting him, how Alexis handles it long term.