The times of the captivity have been rendered illustrious by the predictions and deeds of the prophets, and especially by the remarkable persistency of Daniel in upholding the law, and by the deliverance of Susanna through the divine wisdom, as well as by the other things which it accomplished, and which we shall now relate in their order, Daniel was made a prisoner under King Joachim, and was brought to Babylon, while still a very little child. Afterwards, on account of the beauty of his countenance, he had a place given him among the king's servants, and along with him, Annanias, Misael, and Azarias.
But, when the king had ordered them to be supplied with the finer kinds of food, and had imposed it as a duty on Asphane the eunuch to attend to that matter, Daniel, mindful of the traditions of his fathers which forbade him to partake of food from the table of a king of the Gentiles, begged of the eunuch to be allowed to use a diet of pulse only. Asphane objected that the leanness which would follow might reveal the fact that the king's commandment had been disobeyed; but Daniel, putting his trust in God, promised that he would have greater beauty of countenance from living on pulse than from the use of the king's dainties.
And his words were made good, so that the faces of those who were cared for at the public expense were regarded as by no means comparable to those of Daniel and his friends. Accordingly, being promoted by the king to honor and favor, they were, in a short time, by their prudence and wise conduct, preferred to all those that stood nearest to the king. About the same time, Susanna, the wife of a certain man called Joachis, a woman of remarkable beauty, was desired by two elders, and, when she would not listen to their unchaste proposals, was assailed by a false accusation.
These elders reported that a young man was found with her in a retired place, but escaped their hands by his youthful nimbleness, while they were enfeebled with age. Credit, accordingly, was given to these elders, and Susanna was condemned by the sentence of the people. And, as she was being led away to punishment according to the law, Daniel, who was then twelve years old, after having rebuked the Jews for delivering the innocent to death, demanded that she should be brought back to trial, and that her cause should be heard afresh.
For the multitude of the Jews who were then present, thought that a boy of an age so little commanding respect, had not ventured to take such a bold step without a divine impulse, and, granting him the favor which was asked, returned anew to council. The trial, then, is entered upon once more; and Daniel was allowed to take his place among the elders. Upon this, he orders the two accusers to be separated from each other, and inquires of each of them in turn, under what kind of a tree he had discovered the adulteress. From the difference of answers which they gave, their falsehood was detected: Susanna was acquitted; and the elders, who had brought the innocent into danger, were condemned to death.
Source: Sacred History (New Advent)