Not in the bestiaries (aka, merman!Dean, part 3)
Somebody pounded on the door.
Castiel was out of bed in a moment (though he stubbed his toe on the way), with a gutting knife in his hand. Vikings wouldn’t knock, of course, but sometimes you had to just react before your mind was awake.
“Cass?” somebody yelled, and it wasn’t Gabriel. “You in therre? You’d betterr be in therre. How doess this frreaking thing open?”
Castiel stared at the door. Then he pulled it open, and Dean half-fell forward onto the rushes.
“It’ss about damn time,” he panted, and grabbed at Castiel’s ankle. “You gotta come, man, I need yourr help.”
“It’s two minutes’ walk from the water here,” said Castiel stupidly, blinking down at him.
“Yeah, and it’ss ten minutess’ crrawl, and my belly feelss like sharrkbait and my arrmss feel like sstrring. You coming orr what?”
Castiel scrubbed the sleep out of his eyes, though he wasn’t quite sure he wasn’t dreaming anyway. “Dean. What happened?”
Dean stared up at him, and there was bravado and cheek in his deep green eyes, just like last time, but this time there was real fear as well.
“My brrotherr,” he said. “My little brrotherr, Ssammy. He’ss hurt.”