And then the annoying afterthought arose. Was his work done? Was the proof he had got of Boirac’s guilt sufficient? There was still the alibi. Always that alibi loomed in the background, menacing his success.

Though La Touche had now no doubt Boirac was the man the carter saw, he felt it would be more satisfactory if the two could be brought together in the hope of getting direct evidence of identity. As time was of value he called up Clifford and rapidly discussed the point. It was agreed that, if possible, Hill should be sent to Paris by that evening’s train. A couple of hours later there was a telegram from the solicitor that this had been arranged.

Accordingly, next morning La Touche met the English boat train at the Gare du Nord and welcomed a tall, dark man with a small, close-cut moustache. As they breakfasted, the detective explained what he wished done.

‘The difficulty is that you must see Boirac without his seeing you,’ he ended up, ‘we do not want him to know we are on his trail.’

‘I understand that, sir,’ returned Hill. ‘Have you any plan arranged for me?’

‘Not exactly, but I thought if you were to make up with a false beard and wear glasses he wouldn’t spot you. You could dress differently also. Then I think you might lunch in the same restaurant and come out behind him and see his hand when he’s paying same as I did.’

‘That would do, sir, but the worst of it is I don’t know my way about either in Paris or in a restaurant of that class.’

‘You can’t speak any French?’

‘Not a word, sir.’

‘Then I think I had better ask my man, Mallet, to go with you. He could keep you straight, and you needn’t talk at all.’