Since we found out the truth about Locke last season I have been wetting myself in anticipation of Jack and Locke finally reuniting. We finally got that tonight. And then... The Look.
Their relationship is my favorite of the series. It has transformed so much over time. When they first got to the Island they needed each other. They were co-leaders. It was not a situation that either were fully comfortable with taking the reins. Who really would want to be responsible for 50 people stranded and starving on a deserted Island? Fuck that.
Everything changed when Boone died. Jack knew that John was always going to pursue his own interests over what Jack considered best for the other survivors. John broke the trust and it was never fully healed. It gets immensely more complicated than that. Sparing the details, let's just say "they don't get along".
After they both leave the Island, things change. Locke is dead. Jack takes all the guilt of that situation upon himself. He should have listened to John. He shouldn't have turned him away. Locke was right, and now Jack could never resolve a relationship that he was starting to get some perspective on. Jack undergoes a spiritual awakening of sorts. One that still continues to grow and evolve now that he is back on the Island.
So now there is a Monster wearing a Locke-suit and parading around the Island trying to "save" everyone. A mockery of this once great man. Jack may still be wrestling with his own destiny and struggling to have faith in himself, but he knows that this dude is a bad-guy. And I would hope he is disgusted with the situation.
OK... the point.
The Look on Jack's face.
We know that Jack knows that it's not Locke. That's not a mystery. The mystery is "how does Jack feel about this?"
The Look says it all.
Fear. Intense, mind-blowing fear.
Not necessarily fear of being strewn about the treetops by a pillar of smoke. (That's effing scary though!)
Fear of his own impotence. He's been spending all of this time trying to pathetically piece together this Armor-of-Faith and try to imagine a heroic destiny for himself. But his confidence has been destroyed repeatedly since he left the Island. Every time he tries to build himself back up he finds that he doesn't have the tools necessary to do so.
Sort of like trying to build a plane out of spare parts you'd find on a deserted Island. It won't hold up against turbulence.
So Jack's got this duct-taped sense of purpose, and the minute he sees who he was positioned against, he knew that he was outmatched. All the self-doubt that he's been hiding came flooding out.
John gives him a confident smile. Jack drops a load in his shorts. Perfect ending to the episode.