"Are those your agents whistling?" asked Fandor, as they left the shop.
"No."
"It is, and you'll be able to find your trail by the passers-by who whistle that air."
While talking, the journalist and the detective arrived at the Chateaudun cross-roads. Juve cast an eye over the ground.
"It's six o'clock. Be off and prowl around Notre Dame de Lorette. Loupart will probably come out of that wine-shop you see to the right. You can easily recognise him by his height and a scar on his left cheek."
"Look here, Juve, why should these people whistle 'The Blue Danube' if they are not detectives?"
Juve smiled. "It's quite simple. If you whistle a popular tune in a crowd, some one is bound to take it up. Well, the two men I put to watching Loupart this morning were whistling this same tune, and now we are meeting persons who caught the air."
Fandor crossed the road and proceeded toward Notre Dame de Lorette to the post the detective had allotted to him. The man hunt was about to begin.