The aviators speedily gained an idea of what had happened. That which only the other day they had observed as a solid front of granite and iron on a building covering practically a whole city square had fallen in ruins, completely blockading the broad avenue it had faced.
About the square a cordon had been drawn, and it could be seen, even through the dusk, that troops were spreading fan-shape from this point throughout the entire northern section, while the police darted right and left and everywhere.
The select neighborhood of St. Michael road had not been omitted from the general round-up, the boys found, when they approached the site of the two towers.
It seemed that the abandoned team and wagon had been found somewhere along the highroad, and as suspicion was now acute, the discovery set the fine-comb going along every terrace and police poking in every likely hiding-place.
There had been instant acceptance of the theory that the storehouse and magazine had been deliberately blown up by the cunning contrivance of a spy or spies within the city.
Every stranger must give an account of himself, and even some individuals here and there who were not newcomers.
Billy and Henri could see no opening where two full length military biplanes could alight without notice, and not a morsel of encouragement to try for negotiation on the quiet with the disguised secret agent who had summoned them.
But the aviators hung about, not knowing what else to do for the present, thinking that Roque would make a showing of some sort, as he usually did in tight places.
Flying lower and lower, the two biplanes were sweeping within earshot of the terraced heights along the river front, and though now of dim vision, searching parties could be seen flashing lights up and down the ground tiers.
There was a hullabaloo breaking out on the lowest terrace, immediately overhanging the river—a shot—another and another—like a bunch of firecrackers, so fast did they follow!