“That is my coat, monsieur,” said Servettaz, and as he spoke he lifted it up from the chauffeur’s seat.  “It is Mme. Dauvray’s livery.”

Harry Wethermill groaned aloud.

“We have lost him.  He was within our grasp—­he, the murderer!—­and he was allowed to go!”

Perrichet’s grief was pitiable.

“Monsieur,” he pleaded, “a car slackens its speed and goes on again—­it is not so unusual a thing.  I did not know the number of Mme. Dauvray’s car.  I did not even know that it had disappeared”; and suddenly tears of mortification filled his eyes.  “But why do I make these excuses?” he cried.  “It is better, M. Hanaud, that I go back to my uniform and stand at the street corner.  I am as foolish as I look.”

“Nonsense, my friend,” said Hanaud, clapping the disconsolate man upon the shoulder.  “You remembered the car and its number.  That is something—­and perhaps a great deal,” he added gravely.  “As for the talc mask and the black moustache, that is not much to help us, it is true.”  He looked at Ricardo’s crestfallen face and smiled.  “We might arrest our good friend M. Ricardo upon that evidence, but no one else that I know.”

Hanaud laughed immoderately at his joke.  He alone seemed to feel no disappointment at Perrichet’s oversight.  Ricardo was a little touchy on the subject of his personal appearance, and bridled visibly.  Hanaud turned towards Servettaz.

“Now,” he said, “you know how much petrol was taken from the garage?”

“Yes, monsieur.”

“Can you tell me, by the amount which has been used, how far that car was driven last night?” Hanaud asked.

Servettaz examined the tank.

“A long way, monsieur.  From a hundred and thirty to a hundred and fifty kilometers, I should say.”

“Yes, just about that distance, I should say,” cried Hanaud.

His eyes brightened, and a smile, a rather fierce smile, came to his lips.  He opened the door, and examined with a minute scrutiny the floor of the carriage, and as he looked, the smile faded from his face.  Perplexity returned to it.  He took the cushions, looked them over and shook them out.

“I see no sign—­” he began, and then he uttered a little shrill cry of satisfaction.  From the crack of the door by the hinge he picked off a tiny piece of pale green stuff, which he spread out upon the back of his hand.

“Tell me, what is this?” he said to Ricardo.

“It is a green fabric,” said Ricardo very wisely.

“It is green chiffon,” said Hanaud.  “And the frock in which Mlle. Celie went away was of green chiffon over satin.  Yes, Mlle. Celie travelled in this car.”

He hurried to the driver’s seat.  Upon the floor there was some dark mould.  Hanaud cleaned it off with his knife and held some of it in the palm of his hand.  He turned to Servettaz.

“You drove the car on Tuesday morning before you went to Chambery?”