Oh, no. Lock had not thought to worry about her ability to stay afloat, since she had seemed to be treading water just fine previously. If not that, she had at least kept a good enough grip on the nearest bit of raised land to keep herself from sinking into the icy water. Now, however, she seemed to have utterly lost the energy to keep above the water, or else forgotten that she ought to be doing that in the first place.

"Ah!" he exclaimed as she sank, alarmed. He shifted her little boy on his hip, moving the child farther back and causing the boy to startle and cry — which, honestly, he should have been doing before now anyway. It was possible that only the shock of the cold water had kept him silent before this, but if that was the case the quieting power of the cool had worn off. Lock didn't want to put the baby down, but he also couldn't really get to the woman in the water with only one hand. Even moving the baby back as far as he could on his hip and leaning all the way forward, he could only get his free hand in to the water deeply enough to scrabble for purchase on the wet shoulder of her dress, which was too tight against her skin to have any chance of acting as a proper handhold.

He was hardly going to let the kid wander along the edge of the water alone, though, given what had just happened, and it would take too long to run up to the top of the hill and leave him with Margaery assuming she was even still there, because that was something Lock hadn't gotten around to worrying about yet.

There was no time for second thoughts; Lock lay down on his stomach, still holding on to the boy with one overly muscled arm, and grabbed down blindly into the water, hoping he could find something to hold on to in order to pull the stranger out.