(hb; 1968, 1971: combined, these two books are considered the second part in the theme-linked After Such Knowledge trilogy. Theme-linked sequel to Doctor Mirabilis; theme-linked prequel to A Case of Conscience)
The plot - Black Easter: Theron Ware, a black magick practitioner-for-hire, has been contracted by a mega-wealthy weapons dealer/CEO (Baines) to a series of magickal actions, not the least of which is the unrestrained, mass unleashing of demons.
The "Grand Covenant," which maintains a tetchy détente between white and black magicians, demands that a white magic practitioner ( in this case, Father Domenico) be there to witness - and, if need be, help the black magician (Ware) - rein in the demons at the agreed-upon time.
Of course things go wrong. . .
The plot - The Day After Judgment: The survivors of Black Easter, as well as select military personnel, deal with the global, hellish conflict and chaos set into motion by Ware, Baines, Domenico and others in Black.
These two novels are entertaining, sly-humored, character- and idea-interesting novels, works that take surprising, often quirky turns - filmed as one theatrical release, they would make a fun Seventies-esque b-movie.
Black and Day are worth checking out.