It all seems to dawn on Dexter at once: Deb says he's been good for her, a positive force in her life; Rita said the same. Maybe Harry's wrong; maybe he's not destined to be exactly like Arthur Mitchell. Anyway, Quinn calls Deb inside. Before she heads in, she tearfully tells Dexter she loves him. He looks up at her and speaks with utter sincerity: "I'm so thankful."
After Deb walks off, Dex stands up and spots something in the Mitchell garage. It's the smashed windshield of the Mustang. Arthur must've had it replaced. And recently. He rifles through Arthur's wallet and finds the receipt. So now Dexter has the car he's driving, and the license plate. We cut to Arthur driving the car out of the detail shop before the paint's even dry. Salsa music on the soundtrack reminds us he's still in Miami, for the moment. But the last we see of him, he's taking the open road outta town.
Later, at Miami Metro, Matthews brings in Special Agent Davis and the FBI to meet with Our Heroes. LaGuerta gives the credit to Debra for breaking the case, and Debra starts to get a head of steam about how There Was A Man Called Special Agent Lundy and how he was the one who they should be thanking but now he's dead thanks to Bureau indifference. Davis seems mostly chastened. LaGuerta and the rest of the team bristle at the idea of the Feds taking over the case now that the dirty work is done, but that's life in the big leagues. So Debra's left to watch the room full of Lundy's carefully cultivated evidence get gathered up by the Bureau that never believed him and taken out of her life forever.
Meanwhile...oh wait, I must've sat on my remote control or something...seem to have flipped over to an episode of Supernatural. Wait, no? This is just a long shot down a deserted stretch of road, with mist lying low on the ground like it was carpeted in it, and a classic car bearing down straight toward the camera? ...Okay. So it's Arthur, then, making his grand getaway through the set of The Wolfman when suddenly, his engine starts sputtering. We're all on the same page here, right? That page being several pages ahead? Thankfully, the show doesn't stretch this out: Arthur pulls over and goes to check the engine and discovers he's missing an oil cap. And that's when Dexter, framed in a really gorgeous long shot, comes out from the back seat, slams the hood down on Arthur's head, and, rather than plunging a sedative into his neck, chokes him into unconsciousness. Sometimes, it's the personal touch.