Childhood's End (1953) by Arthur C. Clarke, a sci-fi classic and one of the most memorable books I have ever read.

I pull no punches on the subject of book's controversial ending, so consider yourself warned. If you don't wish to spoil it, watch all the way up till 3:30, then maybe read the book before you watch the rest.

*Links!*

Childhood's End Trailer (Syfy):
https://www.youtube.com/watch?v=i3e7aMCIxjY

Childhood's End on Goodreads:
https://www.goodreads.com/book/show/414999.Childhood_s_End

Buy a new or used copy from this link:
http://www.alibris.co.uk/Childhoods-End-Arthur-Charles-Clarke/book/1053683

Quotes from the book are used under fair use, being as they only contain a potion of the original text, offer further analyses and insights, and are not believed to hurt sales of the book in any way.