Book of Eternity

The Book of Eternity is an ancient artifact of great power. It is the most powerful object in the Post-Hogwarts Continuity. It is currently in the possession of the Batman, who has it locked it away in the Batcave.

Origins
Where the Book came from has not yet been revealed, but it is implied that it is not man-made and came from another planet far away. The Book is incredibly powerful and cannot be destroyed or altered.

Arrival on Earth
At some point, the Book crash landed in Gotham and was put on display in the Gotham museum. At some point presumably between late 2012 and early 2013, it was stolen by crime boss "Knuckles" Konger. He offered to team up with The Scarecrow, who betrayed him and stole the book. He then used it to enslave Konger's men and take over Arkham Asylum. He intended to release an ancient entity of fear called Parallax to aid him in his schemes. However, Parallax did not cooperate and betrayed Scarecrow, taking over his body. The Justice League managed to stop them, and Scarecrow was absorbed into the book.

When General Zod came to earth and destroyed Wayne Manor, he discovered the Book and stole it.

On the night of The Battle of Gotham City, April 5, 2014; Zod (who had been possessed by Parallax) released the Demon Army of Parallax with the Book. After the Battle was won, the Justice League took back the book, and it is currently locked within an vault deep within the Batcave.

On August 12, 2016, Braniac and Sinestro were sent by Darkseid to retrieve the book and free Parallax from the ring. Braniac threatened to shrink the city if the Batman did not bring the Book to him. Batman brought a fake Book of Eternity to Braniac, and learned of the true nature of his plan. Braniac attempted to Shrink the city, in hopes that the book would be revealed to him as the it would not shrink with the rest of the city. However, this was foiled by Plastic Man, and Braniac never gained access to the book.

Trivia

 * The origins of the book will be revealed in time.
 * LEGO Justice League 4 is the first film in the Justice League series not to actually have the book. It was prominently mentioned, and a replica of the book made an appearance, but the actual book remained unseen throughout the entirety of the film.