The basic appeal of this series has revolved around the interactions between Castle and Beckett, but the interactions between Alexis and her dad are a close second. This episode capitalizes on the latter. Molly Quinn steps up and effectively replaces Stana Katic as Castle's investigative partner. Alexis fills Beckett's semi-heroic role.
The mystery is a good one with suspicions moving from one suspect to another. I said that Alexis assumes Beckett's role as one of the key heroines, but Castle has to assume the role of lead investigator. He displays some self-deprecating lack of confidence in this role, which reveals a lot about his character since any fan of the show knows that Castle's experience is more than enough to justify that role, and it is frequently his out of box thinking that leads to case closures. To put my thoughts in another way, this episode gives the writers and viewers a chance to look at the dynamics of main characters in a fresh way.
Meanwhile it is Beckett who sits at home and worries
This episode is far more than a rip-off of other death on airplane murder stories. It is a new look at some of our favorite characters.