That belief has changed, and new findings show they were a smart people, and some believe they were humans, at any rate they eventually bred with humans. Neanderthal DNA can be found in homo sapiens today, and some have that look about them.
These ancient people lived in caves or homes they made with mammoth bones, and were very careful about the way they kept their domiciles. Most could have made the cover of Neanderthal Home and Garden (sorry). They made tools, performed operations, and may have used language and created music.
This book is about a young Neanderthal brought to the future (the future of 1958 when the book was published) and the nurse who learns to love him even though he is an ugly little boy.
No one could say this story shows any signs of political correctness, and some of the words are quite offensive. Ape boy is what the media call him, and he is just a spectacle to be poked at and studied--no one cares that he is a scared little guy except his nurse, who names him Timmie and eventually she loves him dearly.
Ultimately, the company who brought him into the future is ready to send him back where he came from--they want to pull someone else out of time. It doesn't matter to them that he now wears clothes, reads, talks, uses utensils while eating and will be completely lost back in his original home.
It's heartbreaking to think they wouldn't care, but it's believable that corporations and some scientists care for nothing but money and fame, and what's one little boy's life in the shadow of their greatness.
The nurse wants desperately to sneak him out of the building to safety, but she's found out, and so her only recourse, which would be the same as most mothers frantically afraid for their child, is to go back in time with him, and try to keep him safe.
There are many conclusions my mind has created on what happens when they get back and I persist in my belief that she will help him be safe and he will grow to be a great man.
This is a wonderful story and Asimov felt it was one of his best.