the wall that served
as an entrance for the visitors to the ruins. It opened on a sunk road
running between the park wall and a copsewood containing some abandoned
quarries. M. Filleul stooped forward: the dust of the road bore marks
of anti-skid pneumatic tires. Raymonde and Victor remembered that,
after the shot, they had seemed to hear the throb of a motor-car.

The magistrate suggested:

"The man must have joined his confederates."

"Impossible!" cried Victor. "I was here while mademoiselle and Albert
still had him in view."

"Nonsense, he must be somewhere! Outside or inside: we have no choice!"

"He is here," the servants insisted, obstinately.

The magistrate shrugged his shoulders and went back to the house in a
more or less sullen mood. There was no doubt that it was an unpromising
case. A theft in which nothing had been stolen; an invisible prisoner:
what could be less satisfactory?

It was late. M. de Gesvres asked the officials and the two journalists
to stay to lunch. They ate in silence and then M. Filleul returned to
the drawing room, where he questioned the servants. But the sound of a
horse's hoofs came from the courtyard and, a moment after, the gendarme
who had been sent to Dieppe entered.

"Well, did you see the hatter?" exclaimed the magistrate, eager at last
to obtain some positive information.

"I saw M. Maigret. The cap was sold to a cab-driver."

"A cab-driver!"

"Yes, a driver who stopped his fly before the shop and asked to be
supplied with a yellow-leather chauffeur's cap for one of his
customers. This was the only one left. He paid for it, without
troubling about the size, and drove off. He was in a great hurry."

"What sort of fly was it?"

"A calash."

"And on what day did this happen?"

"On what day? Why, to-day, at eight o'clock this morning."

"This morning? What are you talking about?"

"The cap was bought this morning."

"But that's impossible, because it was found last night in the park. If
it was found there, it must have been there; and, consequently, it must
have been bought before."

"The hatter told me it was bought this morning."

There was a moment of general bewilderment. The nonplussed magistrate
strove to understand. Suddenly, he started, as though struck with a
gleam of light:

"Fetch the cabman who brought us here this morning! The man who drove
the calash! Fetch him at once!"

The sergeant of gendarmes and his subordinate ran off to the stabl