A few minutes later, they were several miles out from the shore. Sherlock didn't realize anything was wrong until he felt the land-boy's limbs slacken. Did he want to go back? He glanced over his shoulder at the boy and clicked questioningly, but the boy's eyes were closed, and- he wasn't supposed to be blue, of that Sherlock was sure. Panicked, he kicked his tail hard and broke through the surface of the water, gills on either side of his neck automatically sealing themselves against the harsh dry air.
Sherlock tugged his prize from his back and brought him around to face him. He didn't bother talking to him, because clearly the child couldn't understand him, but checked at the sides of his neck to see if his gills had been shut too long- and found nothing. How did this creature breath? Shaking his head at the folly of letting one's gills close, Sherlock shifted John's weight to one arm and freed his right hand. He ran the tip of his fingernail against his sharp teeth until it was sharp, then quickly cut three fine, nearly invisible gills on either side of the boy's neck before carefully lowering him to submerge them in the sea water.
The boy gurgled and, after a moment, bubbles floated up from his new gills. He coughed, and water dribbled from his mouth- why he had swallowed so much, Sherlock couldn't fathom. He returned his attention to the boy as he shifted and opened his eyes. The mer watched as he raised a hand to his neck, feeling gently at the slits through which he now breathed. He flexed and they sealed shut, and then he opened his mouth and breathed, coughing again to expel some of the brine that had made it's way into his lungs.
Sherlock frowned and shook his head, touching his hand gently to John's lips. He cocked his head, then shook it off. He wasn't all mer, after all. Only partially. He pressed gently at the boy's gills, easing them open again. Than he slipped beneath the waves again. Becoming mer took time, he'd heard. And the boy couldn't do it here.