Sci Fi idea:

An interstellar spacecraft lands on Earth and contains 500 Neanderthals who left Earth 250,000 years ago and travelled in a time dilated circular orbit returning them to Earth.

They did this to skip the ice age.

Neanderthals have larger brains and are smarter than us (eg average IQ is 170) but they are much more nomadic and less social than we are, they obviously had more advanced tech but did not build towns, cities, etc.

Most Neanderthals stayed behind to avoid the awfulness of being on a ship with 500 people.

Only 16 years have passed on the ship, but 250,000 years have passed on Earth.

The Neanderthals return to and discover a civilisation of 8 billion homo sapiens, and 0 Neanderthals.

Trying to figure out what happened, Neanderthals go to various locations on earth and dig up their old societal epicentres (ancient temples) and discover the remains of their descendants who were brutally hunted down a murdered by tribes of homo sapiens.

Tension builds…