The Root Ramayana.
Valmiki had a story in mind and asked Narada for inspiration. Narada told about Rama in 100 verses. These verses are the Mula Ramayana, also called Samkshepa Ramayana. From these 100 verses Valmiki created the 24,000 verses of the Ramayana.
Read Samkshepa Ramayana here
http://stotrarathna.blogspot.com/2009/07/samkshepa-ramayana.html