The novel initially depicts the assassination of a Governor of California (a fictionalized version of Ronald Reagan) by a black magician working as a contract killer.

Black Easter and The Day After Judgment deal with what sorcery would be like if it existed, and the if the ritual magic for summoning demons as described in grimoires actually worked.

Tension between white magicians (who appear to have a line of communications with the unfallen host in Heaven) and Ware is woven over the terms and conditions of a magical covenant that is designed to provide for observers and limitations.

Black Easter ends with Baphomet announcing to the participants that the demons cannot be compelled to return to Hell: the war is over and God is dead.

Algis Budrys was dissatisfied with Black Easter, declaring it, despite Blish's outstanding craftsmanship, to be "an unreasonably inflated short story."

Many of the white magician monks at Monte Albano are named after Blish's fellow science fiction writers: (Black Easter, pp.

The Book of the Sayings of Tsiang Samdup was invented by Talbot Mundy; it is the supposed source of the quotations at the beginning of each chapter in his novels Om — The Secret of Ahbor Valley (1924) and The Devil's Guard (1925).