But Macbeth was in his most belligerent mood, and would not be mollified by soft words. He snarled and barked again, and the twins imagined him circling round his prey.

Suddenly Mary felt the tears sting her eyes - their wonderful work of yesterday for nothing, because somebody had discovered their secret!

"What shall we do, Dickie?"

"It's our camp, isn't it? We found it. You found it - you and Peter, We've had an oath about it and we're in charge now, aren't we? It's an enemy in there, isn't it? We'll go and kill him and tell the others after... We'll do it by ourselves just like we always do... Come on, Mary!"

The twins had not had time to imagine what sort of an enemy they were going to find, but they would never have guessed that he would be young, with laughing brown eyes, and in Air Force uniform with two rings on his blue sleeve, and with wings on his breast. He was sitting on the grass at the foot of the tree with a suit-case and a raincoat beside him, and looking at them in the friendliest way.

"Hullo!" he said. "Is this little chap yours? He makes a lot of noise for a small dog. D'you think you could stop him barking? I wish you would."

Dickie didn't feel quite so sure of himself now. A real enemy he would cheerfully have attacked, but an R.A.F. pilot was a different matter. Then he remembered the oath.

"You're our enemy," he said. "And you're not allowed to stay here. This is private. Nobody is allowed here except us, and it's secret..."

The officer got up.

"I say," he said, "I am sorry, I'd no idea I was trespassing. I was lost, and found this place by chance. I was wondering whether perhaps you'd help a chap in distress?" He looked at Dickie. "It's much easier to fly than to walk, you know. I can find my way in the air, and yet once I start walking I get in the most peculiar places..."

"You're not so much an enemy as we thought, but you can't stay here. This place is ours..."

"Is it a camp?" the stranger asked. "It's a grand place for one. Looks as if you've had a fire here. Can't you tell me all about it, and then I'll tell you about fighting in a Spitfire, if you like?"

Dickie began to weaken. A chap like this could not be a real enemy. He seemed to know all about camps, too.

"What do you want here, anyway?" he asked.

The pilot stooped to pat Macbeth, who was now wagging his tail at him.