Shukracharya was the guru of the demons. One day his
daughter Devyani was taking a bath in a lake with Sarmistha, the
daughter of the demon king, Vishaparva. They had left their clothes on the
bank. Suddenly a strong wind started blowing. They quickly came out of
the lake and put their clothes. By mistake Sarmistha wore Devyani's
clothes. They started fighting. Sarmistha pushed Devyani into a well and
left her there.
After some time King Yayati passes by the well. Seeing Devyani, he
pulled her out. They decided to get married. When Devyani did not return
Shukracharya came looking for her. She refused to go back because the
princess had insulted her. Sukracharya went to Vishaprava and threatened
to leave the kingdom. Vrishaprava begged Devyani for her forgiveness.
Devyani agreed but on one condition - that Sarmistha become her maid.
Soon Yayati and Devyani got married and had three sons. One day,
Sarmistha told Yayati how she came to be Devyani's maid.
Sympathising with her Yayati secretly married her and she had two sons.
When Devyani came to know their secret marriage, she told Sukracharya,
who cursed Yayati with old age. Devyani was very sad at this. Shukracharya
told her that it was not possible to take back the curse but a son of
Yayati could exchange his youth with him.
Yayati requested each of his sons to take away his old age. Only his
youngest son Puru agreed and Yayati become young again. After many years, he realised his injustice towards his son. He returned his son's youth
and made him the king.