"told her the story of Rama, whose beautiful wife had been stolen by the Demon King of Lanka"

Sita is kidnapped by the Demon King
Public DomainSita is kidnapped by the Demon King
The story of Rama and Sita forms part of the ancient Sanskrit epic, The Ramayana

Rama and his wife, Sita, are walking in the forest one day when Sita spots a beautiful deer.  She asks Rama to catch it for her, but as he disappears in pursuit of the deer, Sita is captured by Ravana, the Demon King.  With the help of Hanuman the monkey, Rama must attempt to defeat Ravana and rescue his wife.

You can read the story of Rama and Sita here.