"Not yet!" cried Poke Stover, pointing with his hand to the northwestward. "Thar ye are, Dan!" Dan looked in the direction, and in a patch of cottonwoods made out a white object, moving slowly along. It was the mustang they were after, so tired out that he could scarcely move from one spot to the next. "We've got him now!" ejaculated the youth, enthusiastically. "And just as I was ready to give up, too! Come on!" Away he swept, with all the quickness of which his own wearied steed was capable, and Poke Stover followed him. The white mustang saw them coming, and set off into the timber on a feeble run. The course of the pursued creature was around the northern approach to San Antonio and then toward the Medina River. Many times they thought to give up the chase, but then the white mustang seemed so near and so ready to drop that they kept on until the river bank was gained. Here the mustang disappeared into a pine brake; and it may be as well to add, right here, that neither the Radburys nor Poke Stover ever saw him again. "Where is he?" asked Dan, a few minutes after the animal had disappeared. "Do you think he leaped into the water?" "I heard a splash," answered the old frontiersman. "There it goes again." He tried to pierce the darkness with his eyes. "There is something over yonder, that---- Whoopee, Dan, look!" There was no need for Poke Stover to call the boy's attention to what was on the other side of the Medina, for Dan was already looking, "with all eyes," as the saying is. He had made out a number of Mexican cavalrymen, moving up and down along the west bank, and now he noted two pieces of artillery, which the cannoneers were trying to run out on two rafts moored close at hand. "The Mexican army, as sure as you are born!" cried Stover, in an excited whisper. "Lad, we have made an important discovery. They must be bound for Bexar!" "Yes, and there are thousands of them," answered Dan. His heart was beating so rapidly that he could scarcely speak. "Poke, what had we best do?" "Find out what their game is, first, and then ride back to Bexar as fast as our mustangs can make it. If the garrison isn't warned, there will surely be a great slaughter." There was a stiff norther blowing, making the swollen stream rough and dangerous to cross, and the Mexicans were consulting among themselves as to how they should proceed. With bated breath, the boy and the old frontiersman watched every movement, and, at the same time, tried to figure up mentally how many Mexicans there were. "At least a thousand," said Poke Stover, but, as we know, he was mistaken; the force of the enemy numbered nearly seven times that many, although, to be sure, they were not all in that immediate vicinity. "We will cross the river and investigate," said one of the officers, presently, and a large flat-bottomed boat was brought around and a dozen soldiers leaped into it.