In El Sidrón, a remote, mountainous region of Northern Spain, a tomb of 49,000 year-old Neanderthal bones discovered, leading to an investigation to solve a double mystery: How did this group of Neanderthals die? And, could the fate of this group help explain Neanderthal extinction? Scientists examine the bones--buried over 65 feet below ground--and discover signs that tell a shocking story of how this group of six adults, three teenagers, two children and a baby may have met their death. Some bones have deep cuts, long bones are cracked and skulls crushed--distinct signs of cannibalism. Was it a result of ritual or hunger? Neanderthal experts are adamant that they were not bloodthirsty brutes. Will this investigation challenge their views? What happened here 49000 years ago will take us on a much bigger journey--from El Sidron to the other end of the Iberian Peninsula where scientists are excavating beneath the seas off Gibraltar in search of Neanderthal sites. Scientists working here had theories--but no proof--for why Neanderthals went extinct. El Sidron may change this.