Beast Quest: Soltra the Stone Charmer by Adam Blade

The woman was two heads taller than him, her body swathed in a shining, rippling garment-like a cloak made out of black water. He gazed up into the woman's face-but found that she had no face, just a featureless surface, marble smooth and milky white. Then the final terror came. The whole of her face folded up on itself like a huge eyelid-and from beneath that eyelid stared a single green eye, as green and cleaar as an emerald.