Ok, now द्वारा the end of this लेख (or already at the beggining, because of the title) आप 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...

Pilot [1.1]

Brennan: Tell me आप tried "excuse me" first.
Angela: Ah, Sweetie. Yes, I did. Welcome home. Are आप exhausted? Was Guatemala awful? Was it horribly backward?
Brennan: And yet, I was never reduced to flashing my boobs for information.

Angela: आप know, diving head first in a pit of cadavers is no way to handle a messy breakup.
Brennan: Angela, nothing Pete and I ever did was messy.
Angela: [laughs] Then आप weren't doing the right things.

Brennan: Look, I am sorry if I embarrassed आप in front of your friends, but अगला time आप should identify yourself before attacking me.

DHS Officer:...

This is an idea of mine what season six should be like ... Hope आप like it :)

To Booth and Brennan this was just an usual day. However, it was just the opposite.

In the early morning, Brennan knocked on Booth's apartment door. After waiting a long time in front of them, Booth opened the door wearing only his underwear. He looked tired and cranky.
-You need Sweets to sign your blahblahblah... -That's only what Booth heard from her. After Booth got dressed he and Brennan went to Sweets office. And they caought Sweets and गुलबहार, डेज़ी in ... very awkward position. After they agreed that they will never...