This 1972 novella is quirky in ways I don't often see in contemporary SF. In the 20th century, John Martels, astronomer, slips and falls from the top of his radio telescope. When awareness returns, his consciousness is hosted in a brain-in-a-box 23,000 years in the future. The brain's owner, the Qvant, Supreme Autarch of Rebirth III, can't evict him - and anyway, Martels is a change from endless staring at decaying exhibits in the disused museum where the Qvant is stationed, Rebirth III having given way to Rebirth IV long ago. At intervals, one or another 250th century human visits, to ask the Qvant for advice in their losing war against the Birds - avian species having become larger, smarter, better organized, and much more hostile than in our era. Can the mind from antiquity save the human species from extinction?

The struggle against the Birds is paralleled by Martels' increasing understanding of the psionic forces that brought him to the future and govern the afterlife humans go to. Blish provides a lot of moments where Martels comes to a realization that just is not evident in what the reader knows. I had forgotten how like A. E. van Vogt he could be in this way.

We're also reminded that Blish didn't deserve his reputation as a writer of hard SF, which mainly rested on his having heard of one or two more physicists than most mid-century SF writers. For example, at one point Martels looks at the Moon and notices that it's gotten visibly farther from the Earth over 23,000 years. At 3.8 cm per year, we actually expect less than a kilometer's difference - not visible.

Still, quirky: the psionics, plus various of Blish's hobbyhorses, e.g. that history moves in cycles - the Rebirth eras. So my rating is higher than the story deserves. A newcomer to Blish should skip this one and try "Surface Tension" or A Case of Conscience. ( )