The unlikely Pilgrim, here, is Walt, a fly and grubby urchin on the mean streets of 1930s St Louis, who is talent-spotted by the black-clad Master Yehudi - is he mage or conman? - and trained to walk on air. To enable him to achieve his obvious potential, however, the Master subjects him to a series of grotesque humiliations and tortures. It's a process of spiritual cleansing like that of some extreme mystic sect, and one that's impossible to credit, however high we hung our cynicism at the start. Never mind: one day, from the dog-depths of his despair and loneliness, Walt just takes off. A few inches at first, above the kitchen floor, then gradually a couple of faltering steps, then on to the full over-the-water.
And they're off. A pair of showmen now, Walt the Wonder Boy and the Master bundle around in an old jalopy, raking in the pennies from gawping farmhands at country fairs. You can almost hear the ragtime on the soundtrack.
Nemesis, or gravity's revenge, comes in two guises. There is wicked Uncle Slim, the cruel guardian who handed Walt over to a stranger without a qualm, but who returns for a share of the loot; he is a pantomime villain with real malice in his heart and real bullets in his gun. And there is puberty, which exacts a price for Walt's innocent ability to 'let himself evaporate' so painful that his miraculous abilities, though they do not leave him, can never again be used.
The narrative seems to go Awol in the second half of the novel, perhaps intentionally to reflect Walt's directionless adult life. But as a parable about learning to love, Mr Vertigo is strongly affecting. Its moments of deep feeling are sometimes jammed up against a piece of smart-ass dialogue or jaunty description; at others, though, they are expressed in a way that is as embarrassingly simple as the descriptions of Walt's aerobatics: love is just another miracle, that's all.