TOKYO—In the cramped but orderly lounge of his sixth-floor office in the tony Aoyama district, novelist Haruki Murakami is talking about the diffuse nature of evil in our post-Cold War world.

He muses on Aum Shinrikyo, the Japanese religious cult that poisoned the Tokyo subways in 1995, Al Qaeda and the numerous dead in New York, and on Worm, a monster at the center of the earth with atrophied eyes and a brain that has "turned to jelly as he sleeps," who absorbs and stores the world's hatred. Worm threatens to unleash total destruction in Murakami's calmly bizarre "Super-Frog Saves Tokyo," one of six stories in his new collection, After the Quake (Knopf), in which a resolutely unremarkable man is called upon to battle the darkest forces of evil in a soulless city—by a giant, urbane amphibian.

Quake's narratives are superficially linked by Japan's twin horrors of 1995: the January earthquake in Murakami's childhood hometown of Kobe, and the subway attacks two months later in Tokyo, his hometown since college. But neither event appears directly; all the action takes place in February, the month in the middle.

Instead, it's the characters' discovery of their hollowness, and their often uncertain attempts to fill it, that infuse the book with its meditative power.

After the Quake may be Murakami's most successful marriage yet of a burgeoning social realism—acquired, he says, after interviewing the victims and perpetrators of Aum terrorism for his nonfiction Underground (vol. 1, 1997; vol. 2, 1998), published as a single volume in the U.S. last year—and the fantastical realms of spirit and mind. But as he turns from the fictional Worm to the very nonfictional Aum and Al Qaeda, Japan's most relevant living international man of letters suddenly looks troubled.