The ship has been segregated into different rival domains over the years. Engine is one, and Rule is another. They always linger on the edge of outright war. The story opens with one of Engine's Exalted warriors—a woman named Perceval—being frog-marched as a brutalized prisoner under the hand of Ariane, soon to be the leader of Rule. In her cell, Perceval is tended by a Mean girl named Rien. Rien quickly learns an astonishing secret: that she is Perceval's literal sister, an undisclosed truce hostage of sorts.

Soon Rien has freed Perceval, been Exalted and embarked on a perilous quest across the ghostly ship, where medieval rituals and trappings conceal high-tech underpinnings. (Would you believe, for instance, that a little basilisk named Gavin was once a laser torch?) The two sisters will encounter a necromancer named Mallory, their missing father, Benedick, and ultimately the rival deities Samael—god of Life Support—and Jacob Dust, god of the Archives.

Whom to trust in all this? Maybe no one!

Swordplay mixed with nanotech and AI

Ever since the portrait of the drifting, nescient generation ship sprang full-blown from Heinlein's brain, like Athena from the head of Zeus, SF has had another grand playground in which to enact quest-motif and conceptual-breakthrough stories. Elizabeth Bear, I am sure, is familiar with most prior instances of this scenario, and she strives intelligently with much success to reinvigorate it and make it new. Her language is sharp and strong and playful. Her technology is up to date and cleverly deployed. The cultures she creates are a spiffy blend of futuristic and anachronistic. The plot is never totally predictable. And her characters, including the demiurges, are easy to get next to and relate to.

Taken all in all, this is a fine addition to the generation-ship canon, and will reward your attention with many delights. It strikes me as part of the new resurgence of "planetary romance" SF, found in the work of such figures as Chris Roberson and Al Sarrantonio.

Nevertheless, if I might, I would like to point out a few infelicities.

Giving us two heroines and shifting the tale back and forth between their respective points of view has the effect of diluting the mythological arc of the narrative. (And make no mistake, this is meant to be a fairy tale, as must any story be that starts off with a scullery maid dabbing cobwebs out of a corner while the high and mighty sweep past.) Two quests are not necessarily twice as good as one. And Perceval's quest even has a fatal misstep as written. The awful Ariane, set up to be the bad gal we all love to hiss, is offstage for 90 percent of the book, finally reappearing in an anticlimactic scene where she doesn't even get to metaphorically twirl her mustache before she's dispatched.

But more important, once again as in Bear's earlier work, is the relative pacing here. By the midway point of the book, we have visited only about three or four different circumscribed venues of the vast ship. We won't see much more than that in the second half either. Now, consider Larry Niven's Ringworld (1970). Two hundred and four pages in its latest edition. Try to remember how much strange territory is encompassed in those pages, one-third less than here.

Not everyone has to write or plot like Niven. But if you're going to explore the weird niches of a Big Dumb Object, you've got to get busy, fast!