This is the version found on Wikipedia.
A merchant asked his three daughters what they want him to bring them from the fair. The older two ask for dresses or shawls, but the youngest wants either the feather of Finist the Falcon or a red flower. In some variants, he went to the fair twice, able to bring back what her older sisters had asked for, but not hers, but she did not vary her request.
In the third or first visit, he found the feather, or else found the flower and must promise that his daughter will marry Finist the Falcon for it. Whether the flower or the feather, the thing brought Finist the Falcon to her at night, and he wooed her. If she was given the flower, he gave her a feather that would magically aid her. Her sisters discovered the visit; they might have spied, or she may have appeared in finer clothing, from use of the feathers, than they knew she had, or she may have appeared in church as a strange woman (like Cinderella at the ball) because of her rich clothing, and not hidden it quickly enough when she returned home. Once they became suspicious, they often listened and, hearing a man's voice, tried to persuade their father that their sister had a lover, but failed.
However they discovered it, the sisters put knives in the window, so that he was injured. He said that she must search for him to find him, which would wear out three pairs of iron shoes, and three iron staves. He did not return. She set out to find him.
She finds a hut with a witch (sometimes referred to as a Baba Yaga), who gives her a gift (such as a silver spinning wheel and a golden spindle), and sends her on to another witch. This witch gives her another gift (such as a silver dish and a golden egg), and sends her on to yet a third witch. This one gives her a third gift (such as a golden embroidery frame and a needle that sewed of itself), and sent her to the castle where Finist was to marry.
In some variants, she found someone trying to wash the blood from Finist's shirt and washed it herself. In all, she managed to trade the witches' gifts to the bride to let her stay a night with Finist. The princess either put a magical pin in his hair to keep him asleep or gave him a sleeping draughter; the third night, either Finist is warned not to drink the draught, or the pin falls out. He woke and knew her.
In some variants, he asked the nobles whom he should marry: the woman who had sold him, or the woman who had bought him. They agreed the woman who bought him should have him.
In other variants, she went home to her father. When he and her sisters went to church, she dressed finely and went with Finist, and her sisters came back with stories of the prince and princess who came to church. The third time, her father saw the carriage stopped at his own door, and the daughter had to confess. She married Finist.Otherwise here are longer versions of the story