But he was not. Instead he dashed into the open space in front of the custom house, just as the marines swept by, his hat off and his rifle cracking as fast as he could fire. Seeing that the danger from the marines was past, Donald and Adrian fell in behind Billie, just as an officer came around the corner at the head of another company. Espying the boys, he halted his command. "What are you doing here?" he demanded. "We just came to town," replied Billie, "and we're trying to help avenge the insult to the flag." "Good!" was the emphatic reply. "Fall in behind us. You may be of service." The boys obeyed and followed the company as it swept up the street. Presently they came to a barricade, behind which the marines had taken a stand. The boys expected the command to halt, but instead they passed the barricade and pushed onward toward the outskirts of the city. All the time there was a continuous fire upon them by men secreted on the roofs of houses. "I'd clean out those snipers if I were in command," said Donald to his companions. The words were hardly out of his mouth ere another company of marines made its appearance and the men dashed into the houses on either side of the street. "Somebody has the same idea, Don," was Billie's comment as they rode along. Two blocks farther came the order to halt and entrench. A minute later the officer called the boys toward him. "Would you rather lend us your horses, or act as orderlies?" he asked. "If it's all the same to you," was the reply, "we'll serve as orderlies." "Very well. Will you," turning to Adrian, "go back to the custom house and tell Captain Rush that we have reached our position. You," to Billie, "ride with all speed to the landing and say that the enemy has retreated toward the water works. They should not be allowed to stop long enough to do any damage." The two boys were off like the wind to carry the orders. "Anything for me?" asked Donald. "Not for the present. Better dismount and get behind something." Two minutes later Adrian pulled up in front of the Custom House and delivered his message, while Billie kept on to the water's edge. "Do you know where the water works are?" asked the officer to whom Billie gave his order. "Yes, sir!" "Then lead us to it." Without a word Billie obeyed and the Jackies followed on the run. The information was evidently received none too soon, for they encountered quite a force of Mexicans, guarding the works. A volley from the bluejackets was returned by a scattering fire and the Mexicans turned and fled. But the volley had been sufficient to lose Billie his mount, as his horse came to his knees with a bullet in his shoulder. Without waiting to see the cause of Billie's fall any more than to ask if he was hit, the Jackies pushed on toward the water works, leaving Billie to look out for himself as best he could until the work in hand was completed.