Kyra: the Travelers Duology Prequel

Before Earth had even had tales about merfolk, the supposedly mythical creatures lived technologically advanced lives on a peaceful water planet named Kyra, located too many light-years from Earth for discovery by its unprogressive humans.

For generations, the nobles of Kyra had dutifully followed the protocols to keep their world safe and prosperous, but it only took the selfish ambition of one mermaid to ruin it all. This is the story of how she caused Kyra to fall and forced the merpeople to live on Earth.