Origin stories for all the evil versions of Batman featured in DC's Dark Nights: Metal event. Each origin digs into one of Batman's major flaws as a character (example: his loneliness, his guilt, his paranoia) and tells a story about how those individual flaws send that world's Batman careening over the deep end into villainy. They're not necessary to understand the main plot of Metal. Some are really well done elseworld stories (Murder Machine, Merciless, and The Batman Who Laughs to name a few), but not all of them are winners. Some are either a bit too on the nose or just don’t do anything interesting with their concept (Dawnbreaker has great art but is throughly disappointing).

So here's my recommendation...don’t buy the book. Just look up the individual stories that you're interested in on Comixology and buy them for a buck a piece. Even if you buy all the individual issues, it'll still be cheaper than buying this volume and you can skip over the Dark Knights you aren’t interested in.