‘I don’t know if anyone else actually saw Mr Ponson,’ she answered, ‘but I should think it likely. Probably the door-keeper did, or one of the other men. Have you made inquiries?’

‘No, madame. Not yet.’

‘Well, you had better do so,’ and she got up to indicate that the interview was at an end.

Tanner found himself in the street with a baffled feeling of having handled the interview badly. But it was at least obvious that the lady’s advice was good, and somewhat ruefully he drove back to the Follies.

Here he made exhaustive inquiries, but without any very satisfactory result. The stage door-keeper knew Cosgrove, and said he was a frequent visitor to Miss Belcher. He remembered he had come two or three evenings in the week in question at about 9.30, and stayed with the actress for about half an hour. But he could not be sure whether or not Wednesday was one of these evenings. Three or four other attendants had also seen him, but in no case had there been anything to attract their attention to him, and none of them could say on what nights he had been there. But Tanner had to admit to himself that he could hardly expect such information from persons who were not interested in Cosgrove’s visit.

But on another point he got positive information. His inquiries established the fact that on the Wednesday night of the murder Miss Belcher had been on the stage at 9.15. She therefore could not have been masquerading as Mrs Franklyn’s servant at the Old Ferry.

On the whole the Inspector felt that, in spite of his momentary suspicion of Miss Belcher’s manner, he must fully accept the alibi. The evidence of Cosgrove’s missing the 7.15 p.m. train, and travelling by the 10.30 was overwhelming. The butler’s corroboration of his master’s return to Knightsbridge was convincing. Though Tanner was not so sure of Miss Belcher’s statement, it at least agreed with Cosgrove’s. Further, the lady had not fallen into Tanner’s little trap about the hour of the call and had disagreed with what he told her Cosgrove had said.

Then another point struck him. Cosgrove was at Knightsbridge between 7.45 and 8.00, and at King’s Cross at 10.30. Was this evidence alone not sufficient? Would it have been possible for him to have visited Luce Manor in the interval? Suppose he had used a fast motor and gone by road?

Tanner did not think it could have been done. From London to Halford was thirty-five miles, and there and back made seventy. What speed could he reckon on? Considering how much of London would have to be traversed, and the amount of traffic to be expected on so important a road, Tanner felt sure not more than an average of thirty miles an hour at the outside. This would take two hours and twenty minutes at least, leaving from ten to twenty minutes. The motor never would have risked going up to Luce Manor, as it would have been heard—in fact, no motor did so. That meant that ten minutes must have been spent in going from the road to the boathouse, and another ten in returning. This even if it could be done at all, would leave no time in which to commit the murder, get out the boat and set the body and the oars adrift. Tanner considered it carefully, and at last came to the conclusion the thing would be utterly impossible. Indeed, he did not believe that an average of thirty miles an hour could be maintained. No, the alibi was complete. He felt he must unhesitatingly accept it.

Inspector Tanner was a depressed man as he walked slowly back to New Scotland Yard. Up to the present he saw that he had been on the wrong track—that all his time and trouble had been lost. He was now as far off solving the mystery, as when he started the inquiry, indeed further, for the real scent must now be cooler.