Nobody knew they were hiding among us

Having fled the imminent destruction of Earth, mankind found a new home on the planet Thelios.  Now, 3000 years after settling the planet, the Thelian society is thriving. It is a  society where all basic needs are met, education is highly valued, and information is available to all.  All is going well until an archeological discovery triggers the awakening of something ancient and unexplained.