Usually at the end of a hunt, Dean feels exhilarated, adrenaline coursing through his veins. Today, he just feels tired. That freaking siren, man. It really got him good.

The post-hunt drive is full of regrets. There's so much Dean did wrong today, and he doesn't have anyone to blame but himself. He would have chopped off his own brother's head if Bobby hadn't shown up when he did, so needless to say, he has a lot to ponder as he drives.

Eventually, Sam says a tentative, "Dean?" and pulls him from his thoughts.

"Hmm?" Dean hums, his gaze still on the road ahead.

"Are you sure we're good?" Sam asks.

"'Course."

"Are you sure?" Sam asks again, and it's beginning to feel like he's fishing for a certain answer. "'Cause you haven't said a word to me in hours."

Dean shrugs half-heartedly. "Lot on my mind."

"Like...?" Sam prompts him.

Dean shakes his head. "Don't worry about it."

Sam scoffs. "The only time you ever go this long without talking is when you're asleep or pretending you're not watching embarrassing TV shows. Trust me, I'm worried."

"Well, don't be," Dean says. He glances over at his brother, looking him right in the eye as he says, "It's nothing."

"Dude, you never even turned the radio on," Sam deadpans. "That alone tells me it's not nothing."

Dean reaches over and turns the radio on. He hadn't even noticed it was off. It must've been the siren's doing. He was a little too smitten to notice.

Sam turns the radio off immediately. "Dean, come on. I'm sorry, okay? Now can we talk about this like adults instead of going all 'silent treatment'?"

"No, it's not that," Dean assures him. "Siren's spell. I get it. I said some things I didn't mean, too." He might have meant them deep down, but he doesn't want to start that fight right now.

"Then what is it?" Sam asks.

Dean sighs. He just doesn't know when to stop, does he? "I just can't believe the guy got the drop on me. That's all."

"Dean, he's a siren," Sam says. "Getting the drop on people is what he does."

"Exactly," Dean says. "I knew we were looking for a siren and it never occurred that it could be him. He was at ground zero the entire time and I never..." He trails off, shaking his head.

Sam scoffs. "How were you supposed to know? We thought he lured people in with sex. Obviously you weren't gonna look at your new hunting buddy and think, 'Hey, he's probably a murderous sex monster.'" With a wry smile, he adds, "In any other situation, I'd be glad you decided not to go at it alone. It almost looked like you finally developed a sense of self-preservation."

Usually, a comment like that would have earned either a laugh or an eye roll. This time, Dean doesn't even acknowledge it. Of course that's how Sam sees it. He doesn't even know what lines he could be reading between.

"Look, man," Sam says, "you can beat yourself up over this all you want, but I'm telling you, there's no way you could've known. I mean, you already had a suspect, and it's not like the guy was trying to get in your pants."

"He could've," Dean mutters, quietly enough that he's not sure he expects Sam to hear it.

"What do you mean?" Sam asks, indicating that he did, in fact, hear it.

Dean takes a deep breath, blowing the air out his mouth slowly. "If he'd waited a little longer, if Dr. Roberts didn't pan out, he could've."

"He could've...?" Sam prompts.

Dean looks over at him, exasperated. "'Gotten in my pants,' Sam. I was taking the piss out of you for sleeping with monsters, but the reality is that if he'd actually tried to get in my pants, I absolutely would have gone for it." Hell, if he hadn't offered Nick his flask, they probably would have fucked in the motel, siren case be damned, and that's why he's pissed at himself. That's why he should have known better.

To say Sam looks confused would be an understatement. It takes him a few moments to compose a response, and Dean turns his gaze back to the road while he waits. In all honesty, he's not sure he wants to hear the response. Maybe he shouldn't have started this conversation at all.

Finally, Sam says, "It's still not your fault. I mean, the guy drugged you —"

"And if he hadn't," Dean interrupts, "I still would've slept with him." With a wry smile, he adds, "They weren't lying when they said the siren disguises itself as everything you ever wanted. I was surrounded by half-naked women and all I wanted to do was talk to Nick, strippers be damned."

Sam furrows his brows. "What are you saying?"

"I'm saying I would've fucked him, Sam," Dean deadpans. He's not sure how much more obvious he can make it. "He was obviously too good to be true, but unless he spelled it out for me, I was never going to realize he was the siren."

Sam is silent for a few moments, and Dean almost starts to think they've put an abrupt end to the conversation. He can't say he'd blame the guy; this probably wasn't the conversation he was expecting to have today. It probably wasn't a conversation he was expecting to have, period. Dean can't blame him for deciding he's had enough of it.

Finally, Sam looks over at him, a look of utter exasperation on his face, and all he says is, "That was the weirdest way you could have come out to me and I hope you know I'm never going to let you live that down."