Harry Potter and the Cursed Child is less the eight novel in the series than it is a copy of the script for the stage play of the same name. The book is due out at the end of the month, with a price of $15 (digital) and $18 (paper).
The play focuses on the adventures of Harry's youngest child, Albus Severous Potter:
It was always difficult being Harry Potter and it isn’t much easier now that he is an overworked employee of the Ministry of Magic, a husband and father of three school-age children.
While Harry grapples with a past that refuses to stay where it belongs, his youngest son Albus must struggle with the weight of a family legacy he never wanted. As past and present fuse ominously, both father and son learn the uncomfortable truth: sometimes, darkness comes from unexpected places.
According to the listing, the script book will be available until early 2017, "after which a Definitive Edition of the script will go on sale".
There's no word yet on when or if the script will be turned into a novel, or perhaps an audio production, but the latter is more likely than the former.