About this time the devil, thwarted in his designs, but always on the watch, was permitted to vent his anger against Francesca and her sister-in-law in a way to which he often had recourse, and which, while it seemed to display a momentary power over their bodies, only proved in the end that a stronger one than he was always at hand to defeat his malice, and snatch from him his prize. Francesca and Vannozza had gone to St. Peter's on an intensely hot day in July, in the year 1399. Absorbed in prayer, they had hardly noticed the lapse of time, and twelve o'clock had struck when they set out on their way home. In order to avoid observation, and the marks of veneration which the people lavished upon them as soon as they set eyes on the two saints (as they always called them), they chose the most unfrequented streets they could find. The heat grew intolerable. The sultry air seemed on fire, and not a breath stirred it. Exhausted with fatigue, their mouths parched with thirst, they reached the church of St. Leonardo; and holding each other's hands, approached the brink of the river, in order to cool their burning lips and throbbing heads with a little water. As they bent over the stream for that purpose, a violent blow from an invisible arm was aimed at Francesca, and hurled her into the Tiber. Vannozza fell with her; and, clasped in each other's arms, they were rapidly carried away by the current, and saw no means of escape. "They were lovely in their lives, and in their deaths they were not divided," might well have been said of them, had the watery grave, which seemed inevitable, swallowed up on that day the two brides of the Ponziani. But it was not the will of God that they should perish. Human aid was not at hand; the stream was rapid, the current deep, and the eddies curled around them; but they called upon God with one voice, and in an instant the waters, as if instinct with life, and obedient to a heavenly command, bore them gently to the shore, and deposited them unhurt on the green margin of the river.
About this time also a supernatural favour of the most extraordinary nature was vouchsafed to Francesca. Her guardian angel, who was one day to accompany her, not by an invisible presence only, as in the case of all Christians, but, by a rare privilege of grace, in a visible form, ever manifest to her spiritual sight, now began to reveal himself to her by the most watchful observance of her conduct. At all times and in all places, by day and by night, her slightest faults were noticed and punished by this still invisible, but now evidently present monitor. At the least imperfection in her conduct, before she had time to accuse and to condemn herself, she felt the blow of a mysterious hand, the warning of an ever-attentive guardian; and the sound of that mystical chastisement was audible to others also. Great was the astonishment of those who could thus discern something of God's dealings with this chosen soul. Once, when she had abstained through human respect from interrupting the course of a very frivolous and useless conversation, the warning was inflicted with such severity that she bore the mark of the blow for several succeeding days.