IT was a blistering day in July, and the swell of the sea was like melted lemonade bottles. The twins lay face down on the hot rock, dressed in nothing but overalls. Nicky was squinting at some stars or pin-points of light, which the sun threw on the glittering stone three inches from his nose. By letting his eyes go out of focus, these could be made to swim slowly to the left. Judy was fiddling with a broken egg-shell, admiring its thin, curved, fragile smoothness.