"And what is it that you ought to tell me, my dear?" she asked as her bag slid off her lap to the floor.

Penny picked it up for her and, to Jon's admiration, gazed at the woman with wide, innocent eyes.

"Well," she said, "I've had whooping cough, and we thought..."

"Oh, we did, did we? I've had it too, my dear, so you needn't worry... Now, my boy, come in if you're coming, and don't fiddle about there in the doorway."

Jon flushed with annoyance and squeezing past the big woman's knees he dumped his knapsack on the rack in the far corner.

"Coming over here, Jon?" Penny asked hopefully.

"No, thanks," he said tersely. "I shall be busy on this side for a bit, and I want you to stay over there and write down the numbers of any engines you see. Got the pencil I gave you? And the paper?"

Penny looked out of the window. The train was gliding swiftly now above the squalid rooftops of the South London slums, which for a minute were hidden by a green electric train overtaking them. She fumbled in the pocket of her blazer for a pencil and looked up to catch the large woman's eye. She was not sure, but she thought the stranger winked at her. It was difficult to be certain because her glasses were so thick, but just then a big engine hurtled by on her side and Jon called, "Did you get her, Penny?"

"Oh, I'm so sorry, Jon, but I didn't quite..." she began when the strange woman surprisingly interrupted and called out the number of the engine.

"And here's a pencil, my dear. I always have stacks of pencils" - and she dived into the untidy black bag and produced a handful.

Jon turned from the other window in amazement. "I say," he said, "thanks awfully. That was jolly quick of you. Are you keen on engines?"

"Not a bit," was the answer. "But I'm quick to see things," and there was quite a friendly note in her voice as she smiled at them both.

When the train had left the edge of London behind and was roaring through the suburbs, she asked Jon to get one of her cases from the rack and then produced some chocolate.

"Share it between you," she said. After this it was difficult for them not to be friendly when she spoke to them, and Jon was trying to guess what she was and where she was going when she gave herself away by looking suddenly at Penny and saying abruptly:

"I'd like to sketch you, my child. Can you stay still for a few minutes like that? Look out of the window."

Penny flushed as the woman groped in the bag again and brought out one of the pencils and an old envelope and began to draw with quick, firm strokes.