Ok, now by the end of this article (or already at the beggining, because of the title) you might be calling me crazy.
But my theory is this:
What if Parker wasn't a ghost/hallucination?
I mean, at first I did really believe he was just a figment of Booth's mind, because of the drugs and stuff.
But we do see along the episode that Parker makes physical stuff (like getting an object that was deep in the water, like carrying the lantern, like opening the hatch!) - I mean seriously, what a hell of a good hallucination, that makes that kind of physical stuff.
At first I accepted all this, but when at the end Brennan actually saw Parker and heard him, I mean, didn't any of you actually think that perhaps Parker wasn't dead? And beyond that, that he is the gravedigger? Listen to one more reason for this crazy theory of mine: You do remember on that episode that Sweets said the Gravedigger's character was calm.
That also can be applied to Parker. Remember him saying he was an hallucination, therefore the sense of urgency didn't exist on him? What if it was just an excuse for Booth keep believing he was a ghost? What if Parker was really there, and the calm behaviour of him links him to being the Gravedigger? I mean, even his nickname fits! Grave digger! Parker aparently came from his grave, because even Booth thought him dead.
I mean, I wouldn't call this theory crazy if there wasn't a lot of details to explain, like how Parker managed to get off the ship before the explosion. That's what keeps me hesitating about this theory. And why would Parker fake his death only to years after tell Booth it wasn't his fault that he died...there's still a lot that doesn't fit, but I had to put this idea down here to see if someone else gets the connection, because the "official" gravedigger, that FBI agent...well, I didn't swallow it. It doesn't make sense, that woman being the gravedigger. In my opinion this gravedigger story isn't finished yet.