Looking Glass - Glass Trilogy, #3

Samantha and James Hay have been advised that their missing daughter Gaia have been located in ancient Australia. Dr. Xanatuo, an alien scientist who, along with a lost tribe of Neanderthals and other beings working to help mankind, has discovered a way to send them back in time to be reunited with Gaia. Ernie, the old Aboriginal tracker and leader of the Neanderthals, along with friends Ratana and Nathan and characters from the first two books of the trilogy, will accompany them.
This team of intrepid adventurers have another mission for the journey, along with aiding the Hayes' quest, which is paramount to changing a terrible wrong which exists in the present time.