What's it about?
Enter back into the world of Ciel Phantomhive and his demonic butler. It is Ciel's job, as the Queen's Guard Dog, to police the underworld so they don't become too much of a hassle for the crown and normal citizens. When many children start disappearing and those disappearance coincide with a mysterious circus, what else would you expect? Ciel and Sebastian join the circus to find the children and the story behind the mysterious performers.
Book of Circus is a soft reboot of the Black Butler series. If you're unfamiliar, the first season was enjoyable, but strayed quite a bit from the original story in the manga. Instead of taking the Dragon Ball Z Kai route, this series went a bit more toward Full Metal Alchemist Brotherhood and restarted the story with their most popular arc, using strategically placed flashbacks to remind us of the important pieces. You aren't required to see the first season to understand this series, and you CERTAINLY aren't required to see the second season - in fact, just join the rest of us and pretend that part never happened.
This season brings back the characters you already know and introduces a whole host of new ones who will grow on you. Joker, Beast, Doll and Snake especially are very well written in the short season. You meet each member of the circus and you feel for them, so that makes the inevitable ending that you know is coming that much more painful, as Ciel and Sebastian have a tendency to clean up whatever mess is in front of them and the bodies tend to follow.
I'll be honest it's hard not to spoil the story while talking about it, so I'll keep it vague. Instead I would highly recommend this anime for those who tend to like mysteries and very smart main characters. Ciel is deeply flawed and not the best hero by any means, but you understand where his actions come from and the world he inhabits is always interesting to see. I loved the first season and I still follow the manga through scanlation sites. This anime is a perfect adaptation of the story, with a couple extra scenes added in for that extra punch to the gut, even if you know what's coming.
Seriously, it's a good series. Why haven't you watched it yet? See it. Share it with your friends. Then check out Book of Murder and the rest of the series. But not season 2, just pretend that doesn't exist like the rest of us.