Firstly, can I just say the opening scene of Caskett really adorable? That scene really got me. Who would've thought they were Skyping? I thought they both on Castle's loft. Good one.
Anyway the case of "Need To Know" episode investigates the murder of former star Charlie Reynolds, who was playing on a 90's sitcom called 2 Cool For School. Castle who saw the news and the boys on television rushed to the crime scene and offering his out of the box crime solving mind.
The high profile case must involving Agents Beckett and McCord from Federal Agents to join the investigation for unknown reason about the interest in Reynolds's case. It's Need To Know or restriction of a very sensitive data used by certain organization related to military, etc (Wikipedia). So, Federal Agent needs NYPD to keep reporting everything they know about the case to them but not otherwise.
The involvement of Federal Agents and their strict 'rules' into the case creates tension between Ryan-Espo and Beckett where Castle stand in the middle doesn't know which side he's in. Ryan and Espo finally send Castle to ask Beckett what is Federal Agents up to on this case and when Castle said he does't want to pushing the boundaries, one thing that cracked me up, Ryan said "Castle, your whole relationship is built on a foundation of your boundary pushing." He has a point. And later then there is a sweet-bribing scene on a break room with Beckett did adorable entrance to the room.
As the investigation goes on, it turns out Charlie Reynolds is working for CIA, spying on a Russian mobs Anton Renkov (who also a fan of 2 Cool For School). Since '2 Cool For School' about to be made and financed by Russian, Anton Renkov sees opportunity and was using it to smuggle arms and Charlie's job for CIA was to track those guns.
With evidence they have, it leads Castle and the boys to a girl who had a connection to both Charlie and Anton. Well she has nothing to do with the murder but with CIA interest on Renkov has put the girl life at stake to do a mission, and it made Beckett to do something that can cause loosing her job.
In this episode we are being introduced to the replacement of Beckett on the 12th, Detective Frank 'Sully' Sullivan. He is a short guy with funny face but turns out not really funny, he eats a lot and messy with foods all over his desk. Even Castle not very please with his presence. I don't feel bothered about his presence in the precinct, but it's just weird and I think Castle needs new character with different personality like Sully, so maybe it will bring new aura to the show, as long as he's not disturbing. Not lovable though but we don't know how long he will stick around, so just wait. And Ryan? Oooh really a fanboy of 2 Cool For School. He has the excitement over the show and when Castle read the script and most important of all, THE HAT! "We're gonna need one of these hats, too". Yes, you look great with the hat, Ryan and Espo don't be jealous. We know you loved the show too.