Next came the testing of Austin’s alibi. Though he had made a beginning with this, a great deal remained to be done before he could feel satisfied as to its truth. And satisfied he must be. The circumstances were too suspicious for anything less than utter certainty to suffice.

As he turned the matter over in his mind he slowly came to the conclusion that he could work on these two points simultaneously. The same information would, to some extent at least, be required for both, and the same people would have to be interviewed.

But there was a third point which, equally urgently, required attention. The man who had made the fifth line of footsteps must be traced. And here, again, no time should be lost in getting to work.

Tanner felt he could not take on this inquiry with the others. There was work in it alone for another man. He therefore decided he would wire for an assistant to whom he could hand over this portion of the case.

But as he was here he might as well begin the interviewing of the Manor servants. He therefore left the boathouse, and walked slowly up to the terrace under the great trees of the lawn, past long herbaceous borders, and through the Dutch garden with its geometrically shaped beds, its boxwood edgings, and its masses of rich colour. Approached from the front, the old house looked its best. Though somewhat heavy and formal in detail, its proportion was admirable, and it had an air of security and comfort strangely at variance with the tragic happening which had overtaken its owner. Tanner labelled it one of the ‘stately homes of England’ as he crossed the terrace to the ornate porch and pulled the bell.

Parkes opened the door. The Inspector introduced himself, and courteously asked for an interview. With equal politeness, and an evident desire to help, Parkes brought his visitor to his own sanctum and told his story. But to Tanner most of it was already known. Indeed, on a very few points only did he add to his knowledge of the case.

The first was that on the previous Friday, five days before his death, Sir William had become depressed and irritable, as if some trouble was weighing on his mind. The change had occurred quite suddenly between breakfast and lunch and had continued until the end. To Parkes the cause was unknown.

The second matter was more interesting and suggestive, but less tangible. When Tanner was interrogating the butler about Austin Ponson he noticed that certain of the latter’s replies were not so spontaneous as those to earlier questions. In particular, when he asked whether during his call at Luce Manor on Sunday evening Austin had seemed worried or depressed, Parkes, though he replied in the negative, seemed so uncomfortable that the Inspector began to doubt if he was speaking the truth. He was not certain, but the thought crossed his mind that the butler knew something which he was holding back. At this stage Tanner was anxious not to arouse suspicion that he was interested in Austin. He therefore changed the subject and made inquiries about Cosgrove. But of him he learnt nothing except that he had not been at Luce Manor for over a month.

From the butler Tanner found out also that neither Austin Ponson nor anyone at Luce Manor smoked dark-coloured cigarettes.

The Inspector next interviewed Innes. Having heard the valet’s statement, which was almost identical with Parkes’s, he began to question him in the hope of learning something further.