Catherine straightened her back and looked out over the sea. Opal, immobile, so clear that the flat pink ledges beyond the lowest tide mark were like blocks of pigment in the water. Something strange in this dark of the moon tide, dragging the water away from hidden places, uncovering secret pools. Once every summer Catherine rowed across to the small rocky point that marked the entrance to the cove, to see what the tide disclosed. There was a thrill about the hour when the water seemed to hang motionless, below the denuded rocks. Spencer felt it; Catherine had touched the sensitive vibration of his fingers as he searched. Marian found the expedition interesting, like clam digging! Catherine remembered the year the fog had come in as the tide swung back, suddenly terrifyingly thick and gray about them, so that she had wondered whether they ever would find their own mooring; she could see the ghostly shore, with unfamiliar rocks looming darkly out of the grayness, as she rowed slowly around the cove, trying to keep the shore line as guide. Charles had come out to meet them; his "Hullo!" had been a whisper first, moving through the mist and seeming to recede. Then he had come alongside them, the fog drops thick on his worried face. Spencer had liked that, too, although Marian had crouched on her bow seat, shivering. No fog to-day. The horizon line was pale and clear. She should go back for Letty. They had left her behind them on a sandy stretch of beach, with a pile of whitened sea-urchin shells. "Mother!" Spencer repeated his summons. "What is dark o' the moon?" Catherine explained vaguely as they scrambled up the rounded, slippery rocks to the patch of coarse grass at the top of the small point. Where was Letty? She had been visible from there. Catherine began to run, down to the muddy flats that separated the point from the mainland. Only a few minutes since she had last seen her head, like a bit of bright seaweed. The water was so far out, surely---- Panic nipped at her heels as she flew. "Letty! Let-ty!" There was the pile of shells. "Letty!" A spasm of fear choked her breathing. Then a call, deep and contented. "Letty here." Around the clump of beach peas and driftwood-- The yellow head nodded out of a mud hole left by a clam digger on the beach. "Letty swim." Catherine picked up her daughter. "Letty, darling! You little imp----" The gray mud dripped from rompers and sandals. "Oh, she's all wet." Marian puffed up. "And dirty!" "Now how are we going to get you home without a cold, young woman!" Catherine stood her on the beach, and sighed. Letty, her fingers full of the soft mud, looked up with bright, unremorseful eyes. "My sweater's in the dory, Mother." Spencer frowned at his sister. "You haven't any sense, Letty."