Two horses turned back rearing, and dashed away, but the third was gripped by a strong hand; and before the party behind could see a vestige of what was happening, two riderless horses had galloped past them, throwing them into a panic of confusion and terror.
Lord Claud had judged right in part.

Thrown into confusion, the men turned as if to flee, thinking themselves fallen amongst a large band of robbers.

Tom made a quick rush round the corner, seized the second pack horse by the bridle, and dashed off in pursuit of Lord Claud; but even as he did so he became aware that there were more than the two troopers in the party, and in a moment the sound of yells and cries behind him told him that he was pursued.
But he had proved the pace of the horse beneath him, and if he could but possess himself of the bags upon the pack horse, and let the slower-paced beast go free, he knew he could distance pursuit.
With a mighty effort he lifted the heavy bags and swung them over his shoulders; but even at that moment he heard the crack of firearms in the rear, and his good horse reared up perfectly erect, and Tom had but time to slip off his back before the creature fell over backwards, and lay still and dead.
Tom had another pistol, and even as he reached the ground he turned round and fired full at the foremost pursuer.

A cry of pain told him his shot had found a billet in horse or man.

But he could stay for no more.