Things are getting crazy for our man Dex after he found Arthur trying to pull a Han Solo on that poor little kid. Arthur tries to track him down, or track Kyle Butler down, and give him the old what for. The old what for in this case is, of course, murder.
The detectives, meanwhile, interrogate old Christine about her relationship to Trinity, and she stonewalls. She is really devoted to her awful father, apparently. Dexter sees how close they are to finding Arthur, so decides to throw them off the trail by framing a trucker with a history of killing prostitutes. He finds him, murders him, and plants Arthur's DNA (handily stolen from the Mitchell household) all over the trucker's house.
Arthur has also been calling Dex, trying to figure out who he really is, and Dexter turns it around, saying he'll go to the police with the fact that Arthur is a pedophile (not actually true) if Arthur doesn't give him $50,000. Of course, Dexter doesn't really want the money - he wants Arthur's blood.
Christine is released from the station, since they don't charge her, and she frantically calls Arthur, looking for help and guidance. Arthur tells her to never call again (Father of the Year!) and Christine is distraught. She calls Deb over, confesses to killing Lundy and injuring her, then shoots herself. Yikes.
Dexter is trying to catch Arthur in an amusement park (no doubt trying to abduct another little boy), but when Deb calls him away, Arthur sees him and follows him back to the police station! After some detective work of his own, Arthur figures out that Dex is in the homicide division, and wanders up there with a stolen visitors' pass. He meanders into the Trinity room, where all his victims' pictures are laid before him. Arthur laughs maniacally.
Let's pause for a second. Imagine you are a police officer in Miami. You see a strange man who fits the exact profile of the Trinity killer (based on the DNA evidence gathered) laughing maniacally while surveying all the evidence. Do you:
A) alert the head of homicide while subtly blocking all exits
B) walk into the room and inquire what exactly this dude is doing
C) stroll casually by and not take any action
Apparently, Miami Metro protocol is C, because no one did ANYTHING. Eventually, Dexter catches sight of Arthur, and they have a confrontation in the middle of the homicide room. Again, there are several things Dexter could have done in this situation, but his motivations for not doing them are clear. If Arthur is accused within the frames of the law, Dexter cannot exact his justice, and there's a chance Arthur will get away with his crimes. So, paradoxically, it's better for Dexter to protect Arthur from the long arm of the law. Anyhow, they meet in the middle of the homicide area, Arthur reads Dex's badge, and the last line of the episode is, of course, "Hello, Dexter Morgan." The end!
And now we're all set for the finale - all the pieces are set in motion, everyone's secrets have been revealed. Oh, and Angel and LaGuerda are married now, as if you cared. Next up: finally killing Trinity? Let's hope so - because somebody is going down in this battle, and if it's Dex, this show will become a whole lot less watchable.