black easter is a fantasy novel by american writer 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 novellas form the third part of the thematic "after such knowledge" trilogy (the title is from a line of t. s. eliot's "gerontion": "after such knowledge, what forgiveness?") with "a case of conscience" and "doctor mirabilis". blish has stated that it was only after completing "black easter" that he realized that the works formed a trilogy.