“Nor I,” Luttrell agreed with a despairing vehemence, “but we can’t prove it.  Jenny Prask is going to know nothing of that key.  ’No, no, no, no!’ she is going to say, ’Ask Miss Whitworth!  Miss Whitworth came back from Harrel.  Miss Whitworth was the last person to see Mrs. Croyle alive.  Ask her!’ It is Jenny Prask or Miss Whitworth.  We are up against that alternative all the time.  And Jenny holds all the cards.  For she knows, damn her, what happened here last night.”

“She did hold all the cards this morning,” Hillyard corrected.  “She doesn’t now.  Look at this key!  There was a heavy dew last night.  It was wet underfoot in the garden at Harrel.”

“Yes,” said Millie.

“How is it then that there’s no rust upon the key?” and as he asked the question he twirled the key so that the light flashed upon stem and wards until they shone like silver.  “No, this key was placed where you found it, Luttrell, not last night, but this morning after the sun had dried the grass.”

“But we came home by daylight,” Sir Chichester interposed.  “They might argue that Joan might have slipped downstairs before she went to bed, with the key in her hand.”

“But she wouldn’t have chosen that spot in front of the library window.  She might have flung it from her window, she might conceivably have slipped round the house and laid it under Mrs. Croyle’s window.  But to place it in front of the library to which room she returned from Harrel—­no.”

“Yes,” said Sir Chichester doubtfully.  “I see.  Joan can make good that point.  Yes, she can explain that.”  And Millie Splay broke in with impatience: 

“Explain it!  Of course.  But what we want is to avoid that she should have to explain anything, that she should be called as a witness at all!”

There lay the point of trouble.  To it, they came ceaselessly back, revolving in the circle of their vain argument.  Joan had something to conceal, and Jenny Prask was determined that she should disclose it, and Jenny Prask held the means by which to force her.

“But that’s just what I am driving at,” continued Martin.  “We can’t afford to be gentle here.  There’s no lie Jenny Prask wouldn’t tell to force Joan into the witness box.  We have got to deal relentlessly with Jenny Prask.  A woman’s voice spoke from this house over the telephone to London at a quarter-past twelve last night, and said that Stella was dead.  Whose voice?  Not Joan’s.  Joan was having supper with Luttrell at twelve o’clock.  I saw her, others, too, saw her of course.  Whose voice then?  Stella’s, as we say—­as we know.  But if not Stella’s, as Jenny Prask says—­why then there is only one other woman’s voice which could have given the news.”

“Jenny’s,” cried Millie with a sudden upspring of hope.

“Yes, Jenny Prask’s.”

Millie Splay rose from her chair swiftly and rang the bell; and when Harper answered it, she said: