Blish created a trilogy, each volume of which dealt with an aspect of the price of knowledge, & gave it the overall name of After Such Knowledge (from a T.S. Eliot quote). The 1st published, A Case of Conscience (winner of the '59 Hugo Award as well as 2004/1953 Retrospective Hugo for Best Novella), showed a Jesuit priest confronted with an intelligent alien species, apparently unfallen, which he eventually concludes must be a Satanic fabrication. The 2nd, Doctor Mirabilis, is a historical novel about the medieval proto-scientist Roger Bacon. The 3rd, actually two short novels, Black Easter & The Day After Judgment, was written using the assumption that the ritual magic for summoning demons as described in grimoires actually worked. In that book, a powerful industrialist & arms merchant arranges to call up demons in the midst of a modern world crisis, resulting in nuclear war & the destruction of civilization. Black Easter is devoted to that element of the plot; The Day After Judgment is devoted to exploring the consequences of the destruction of the world, with an extraordinary ending in both narrative & theological terms.

Black Easter is a Nebula Award-nominated fantasy novel by James Blish in which an arms dealer hires a black magician to unleash all the Demons of Hell on earth for a single day. It was first published in 1968. The sequel is The Day After Judgment. Together, those two very short novels form the third part of the thematic "After Such Knowledge" trilogy (title from T.S. Eliot's "Gerontion," "After such knowledge, what forgiveness?") with A Case of Conscience & Dr. Mirabilis. Black Easter was serialised as Faust aleph-null in If magazine.

Theron Ware and Father Domenico are left to combat the evil forces unleashed on Black Easter

Father Ruiz-Sanchez is a dedicated man—a priest who is also a scientist, and a scientist who is also a human being. He has found no insoluble conflicts in his beliefs or his ethics . . . until he is sent to Lithia. There he comes upon a race of aliens who are admirable in every way except for their total reliance on cold reason; they are incapable of faith or belief. Confronted with a profound scientific riddle and ethical quandary, Father Ruiz-Sanchez soon finds himself torn between the teachings of his faith, the teachings of his science, and the inner promptings of his humanity. There is only one solution: He must accept an ancient and unforgivable heresy—and risk the futures of both worlds . . .

A cloistered monk desperately tries to close the Pandora's box opened by a mischievous weapons dealer who has recruited a powerful black magician to stir up trouble for humanity on the eve of Judgement Day