Peter looked back towards the top of the valley, and then gripped his arm. "The sun has gone... we're going to have Mynd mist. You'd better hurry home, David. Shall I come with you or can you find the way now?"

"No need for you to come, Peter. Of course I can manage. Straight down here into the lane where I tried to ride Sally, and then turn right till I come to the track round the hill to Ingles or go a little farther and cut through to Witchend. It looks as if it's worse at the top."

"Yes, it is, but I could find my way blindfold. It's just that Father will worry... Very well. Good-bye, Captain. See you here to-morrow if it's fine enough for a swim, and if not I'll ride over to you," and she grinned and saluted him before turning back into Hatchholt.

David hurried on. It was cold now, and the hilltops were hazy, but he reached the lane without difficulty. All was very still. Even the birds were quiet, and the world seemed to be waiting for something unknown. When he put a hand to his pocket the tweed of his jacket was damp. The road grew more indistinct, and the cold white mist came rolling silently down from the hills. He passed the track to Ingles knowing that he must go straight home now, but just before he reached the short cut which Peter had shown him that morning, he stopped in surprise. Faintly, yet unmistakably, there came the sound of an aeroplane. It was difficult to guess its direction, but suddenly the heavy air throbbed fiercely as the machine passed nearly overhead and David spared a thought for the unfortunate pilot caught in such weather, and wondered how he would find his way back to his aerodrome when all he could see was a flat soft surface of billowing cotton-wool. He wondered, too, how he would avoid the hills if he couldn't see them. As he hurried along the path by the sodden bracken, the noise of the engine died away, and when at last he came to their own familiar white gate, the silence was complete again.

As he raised the latch of the front door he called out cheerfully: "Here I am, Mother. Hope you weren't worried about me. How is Mrs. Ingles, and what have the twins been up to?"

Mrs. Morton came out of the living-room at the sound of his step, with her usual happy smile of welcome. As he spoke, the smile faded and she said quickly, "Aren't the twins with you, David?"

He shook his head.

"But they must be. You're not playing a game with me, David old chap? They're not hiding outside in the mist, are they?"