But suddenly Gambaru touched his arm.
"Dat's dem, sah!" he cried, extending his arm. For a few moments Royce's less perfect vision failed to descry anything upon the track except what seemed to be a slight haze. But at length he was able to distinguish figures, and then he felt considerable surprise. The men he saw marching towards him were all on foot. Where were the horsemen whom he had previously seen at the head of the column?
"What uncommon luck!" he said to himself. "They seem to have left the track already, and gone to one side or the other to cross by some ford they know. It makes things easier."
He had expected the mounted men to accompany the column to the bridge, and then part from it to find the ford. That they had not done so proved, first that they were very confident, and secondly that the ford was at some considerable distance from the bridge.
The Tubus clearly expected no molestation by natives of the district, whom they, no doubt, regarded as completely cowed. It was equally clear that they intended, after making their detour by the ford, to meet the rest of the column at some spot beyond the bridge.
Taking care to keep under cover, Royce watched the procession until the last man appeared. All the horsemen had gone. He made out that there was a vanguard of about half a dozen armed men, and another half a dozen brought up the rear. At intervals along the column there were about the same number, acting as escort to the prisoners. The vanguard marched some two hundred yards ahead of the rest, who were strung out over at least half a mile. They marched very slowly.
It was a long time before Royce was able to distinguish the figure of his friend. He almost feared that Challis had been taken to the ford, still tied to the saddle; and it gave him a thrill of joy when at last he observed the white-clad form, about half-way down the column.
Royce had already conceived the general idea of his ambuscade; the absence of the horsemen promised to make its working out in detail much easier than he could have hoped. These details he thought out as he watched the column slowly advancing.
His plan was to let the vanguard pass over the bridge, then to sever them from the rest of the column by cutting the remainder of the ropes, and afterwards to deal with the others as circumstances might dictate. It was this last part which had given him most anxiety. Now, however, he rapidly made up his mind to attempt an operation which had been suggested by the nature of the ground.
The track, it will be remembered, made a sharp bend just where it descended to the river. On one side was the river itself, thickly fringed with rushes; on the other, the steep and almost precipitous slope. It depended on the nerve and the quickness of Gambaru whether he could take advantage of that bend to carry out his scheme.