Description from Amazon:
King Bela and Queen Maria Lascaris stood trapped on the Island of Trau, at the mercy of the Tartar forces encamped on the shore. The fate of Hungary lay perilously before them. Bela recoiled in the grips of despair, but his wife proffered that they might yet obtain God's favor and save Hungary if they were to dedicate the unborn child in her womb to God and Saint Dominic as a peace offering. Having made their vow, the King and Queen of Hungary awoke on the third day to find that the Tartar forces had vanished in the night. Hungary was saved. What follows is the story of the child consecrated to God from her mother's womb. Princess, Nun, and Saint: this is the life of Margaret of Hungary.