This is a summary. To read the whole story subscribe to BostonGlobe.com
E.L. Doctorow’s twelfth novel, “Andrew’s Brain,” begins a step from cliché, with a man carrying an infant to a door in the snow. The man is the titular Andrew, the infant his own with recently diseased second wife Briony, and the doorstep that of his ex-wife Martha. Of course, he leaves the infant there.