'Whether or no that's done, you shall have the plan, Lady Wardrop. I have made one, and no later than tonight I can trace you a copy.'

'Admirable: a pencil tracing will be all I want, with an indication of the scale. I can easily have it brought into line with the rest of my plates. Many, many thanks.'

'Very well, you shall have that tomorrow. I wish you could help me to a solution of my block-puzzle.'

'What, those stones in the summer-house? That is a puzzle; they are in no sort of order? Of course not. But the men who put them down must have had some directions—perhaps you'll find a paper about it among your uncle's things. If not, you'll have to call in somebody who's an expert in ciphers.'

'Advise me about something else, please,' said Humphreys. 'That bush-thing under the library window: you would have that away, wouldn't you?'

'Which? That? Oh, I think not,' said Lady Wardrop. 'I can't see it very well from this distance, but it's not unsightly.'

'Perhaps you're right; only, looking out of my window, just above it, last night, I thought it took up too much room. It doesn't seem to, as one sees it from here, certainly. Very well, I'll leave it alone for a bit.'

Tea was the next business, soon after which Lady Wardrop drove off; but, half-way down the drive, she stopped the car and beckoned to Humphreys, who was still on the front-door steps. He ran to glean her parting words, which were: 'It just occurs to me, it might be worth your while to look at the underside of those stones. They must have been numbered, mustn't they? Good-bye again. Home, please.'

* * * * *

The main occupation of this evening at any rate was settled. The tracing of the plan for Lady Wardrop and the careful collation of it with the original meant a couple of hours' work at least. Accordingly, soon after nine Humphreys had his materials put out in the library and began. It was a still, stuffy evening; windows had to stand open, and he had more than one grisly encounter with a bat. These unnerving episodes made him keep the tail of his eye on the window. Once or twice it was a question whether there was—not a bat, but something more considerable—that had a mind to join him. How unpleasant it would be if someone had slipped noiselessly over the sill and was crouching on the floor!