"I wonder," he said between his teeth. "I wonder why that door stuck?"

He examined it minutely, shutting and opening it. It fitted perfectly.

"One picture more," he said with a sigh. "Will you loop back that rose curtain, Mademoiselle Elise? Thank you. Just hold it so."

The familiar click occurred. He handed a glass slide to Elise to hold, relinquished the tripod to Tuppence, and carefully readjusted and closed the camera.

He made some easy excuse to get rid of Elise, and as soon as she was out of the room, he caught hold of Tuppence and spoke rapidly.

"Look here, I've got an idea. Can you hang on here? Search all the rooms-that will take some time. Try and get an interview with the old bird-Lady Laura-but don't alarm her. Tell her you suspect the parlormaid. But whatever you do, don't let her leave the house. I'm going off in the car. I'll be back as soon as I can."

"All right," said Tuppence. "But don't be too cocksure. You've forgotten one thing."

"What's that?"

"The girl. There's something funny about that girl. Listen, I've found out the time she started from the house this morning. It took her two hours to get to our office. That's nonsense. Where did she go before she came to us?"

"There's something in that," admitted her husband. "Well, follow up any old clue you like, but don't let Lady Laura leave the house. What's that?"

His quick ear had caught a faint rustle outside on the landing. He strode across to the door, but there was no one to be seen.

"Well, so long," he said. "I'll be back as soon as I can."