Five minutes later, with a smile that played uneasily over a face grown gray with anxiety, Carl presented the map to the tallest of the three strangers.

It was open so that the pencil marks were most obvious.

By his accent it was evident the tallest of the three strangers was an American.
"What the devil!" he protested; "which of you boys has been playing hob with my map ?" For just an instant the two pink-cheeked ones regarded him with disfavor; until, for just an instant, his eyebrows rose and, with a glance, he signified the waiter.
"Oh, that!" exclaimed the younger one.

"The Automobile Club asked us to mark down petrol stations.

Those marks mean that's where you can buy petrol." The head-waiter breathed deeply.