Let us call these two the known pair and the secret pair. On the evening of the murder, then, Austin puts on the known pair which the butler had in his charge, goes to Luce Manor, commits the murder, walks home through some muddy ground, gets the shoes wet, changes them on returning home, where they dry during the night and are cleaned by the butler next day, all exactly as the latter had stated. But at some other time, probably in the dead of Wednesday night, Austin gets up, puts on the other pair—the secret pair—and slipping out of his house unnoticed, makes the tracks at the Abbey. To make the deception more convincing he has previously dinted the sole of one of these ‘secret’ shoes, so that this dint will show on the prints at the Abbey. At some convenient opportunity when the butler is out of the way he himself cleans the secret pair, and then changes them for the others. The dinted pair which made the tracks at the Abbey thus become those in the butler’s charge; the others, in which the murder was committed, are locked away by Austin, who doubtless takes an early opportunity of destroying them.

Tanner had to admit the ingenuity of the plan. To anyone not knowing there were two pairs of shoes in question, the alibi would be overwhelming.

But completely to prove this theory it would be necessary to show that Austin was at the Abbey at some time other than that he had stated. It was with this object Tanner was returning to Halford.

He made most persistent inquiries, but was unable to find any evidence on this point. None of the cottagers nor farm hands in the vicinity of the Abbey had seen Austin, either on the Wednesday evening or at any other time. Nor had any other stranger been observed. If, however, Austin had been to the Abbey in the middle of the night, as Tanner suspected, the failure to see him was not surprising, and did not invalidate the main conclusion. On the contrary, Tanner believed he had solved his problem. Austin, he felt, was guilty beyond a shadow of doubt.

And then Tanner saw that this solution cleared up another point by which he had been somewhat puzzled, namely, Austin’s readiness, indeed almost eagerness, to tell of his visit to the Abbey. That, he now saw, had been a trap, and he, Tanner, had walked right into it. He saw Austin’s motive now. From the latter’s point of view it was necessary that Tanner should inspect the footprints while they were still fresh. If some days passed before suspicion was aroused, the marks would have become obliterated, and the alibi worthless. Austin was a cleverer man than the Inspector had given him credit for. By his manner he had deliberately roused the latter’s suspicions so that his alibi might be established while the footprints were clear.

That evening Tanner made careful notes of the evidence he had accumulated against Austin Ponson. When the document was completed, it read:

  1. Austin never got on with Sir William.
  2. Though Sir William allowed him £1000 a year, this was a small sum compared to what he might equally easily have paid.
  3. Austin could not be making more than two or three hundred a year, so his total income could not much exceed £1200.
  4. He was living up to, or almost up to, this figure.
  5. Austin had become engaged to a girl to whom, as a daughter-in-law, there was every reason to believe Sir William objected. This girl had no dot.
  6. Unless he got an increased allowance Austin would find himself very pinched after marriage.
  7. Sir William had threatened that if the marriage came off, he would not only not increase the allowance, but might alter his will adversely to Austin.
  8. Austin would therefore be faced with the alternative of having his prospects ruined if his father lived, or, if he died, of receiving £150,000. Thus not only his own position and comfort were at stake, but that also of the girl he loved—a terrible temptation.
  9. Austin had an interview with Sir William on the Sunday night previous to the murder, at which the two quarrelled about a lady—presumably Miss Drew.
  10. Austin had the requisite knowledge of Luce Manor and Sir William’s ways to have accomplished the deed.
  11. Austin had on that Wednesday night rowed down the river and met Sir William at the Luce Manor boathouse.
  12. Austin had denied having been in the neighbourhood at the time.
  13. Austin had invented and carried out an elaborate plant with the object of proving an alibi. This alibi was a deliberate falsehood from beginning to end, and was prearranged.

As Tanner read over his document he felt that seldom had he investigated a clearer case, or got together more utterly damning evidence.

‘The man’s as good as hanged,’ he said grimly to himself.

Next morning he laid his conclusions before his chief, with the result that an hour later he was again on his way to Halford, armed with a warrant for Austin Ponson’s arrest.