His new subject, too, mirrors Stuart, in so far as Norton, like Stuart, has an unusual cast of mind and he is not an easy fellow to nail.
Norton is, as the book opens, Masters' landlord. At first he appears to be a mess living in a mess, a shaggy haired slob who eats little more than tinned mackerel and boil-in-the-bag rice and whose rooms - "the excavation" - are filled with bags and bags of old rail and bus timetables. He carries, at all times, a bag clutched in the crook of his arm. He eats a lot of bhuja mix, and has, according to Masters, five distinctive grunts.
But Norton was also one of the greatest mathematics prodigies of last century, who completed his first degree while at Eton, before going on to Cambridge where he was among an elite group which created a bible for number theory and worked on some extraordinary problem called "the Monster". He was a genius among geniuses.
And then, in 1985, he seemed to have some sort of breakdown, more or less leaving Cambridge to campaign for public transport and collect all those timetables.
The trap would be to write Norton off as some sort of eccentric boffin. But Masters is smarter than that. Instead he spends 350 pages trying to understand who this prodigy now is, and how and why he might appear to have walked away from his talent in order to live in a tip, collect timetables and take trips to godawful places like Woking.
There is another layer too. Norton is more than just the subject here, he is a commentator and participant too. The manuscript, as it developed, seems to have been passed back and forth between biographer and biographee, so that we have Norton correcting Masters, stating the facts of his life as he sees them, and arguing that the author pretty much doesn't know what the hell he's doing.
If this makes the book as messy as its subject - and at times Masters' clever-clever devices are a little too cute by half - it does ask the reader not only to reflect on what genius is but to consider the complexion and construction of biography too.
It's an odd book, all right, and for the most part an entertaining one.