If a poll were taken of such things, the all-time blues crown would inevitably be laid on one Robert Johnson. The bluesman’s bluesman, Johnson is as much a figure of myth as record: pictures are few, a legacy built on just a handful of primitive recordings and an early death (reportedly poisoned for his renown philandering). His talent though, the essential genius of the man, lies in a Faustian pact with the Devil: in exchange for his blues prowess, Robert Johnson sold his eternal soul at the crossroads one dark night.

Mosley’s novel opens on an old black man, Atwater - Soupspoon - Wise being thrown out of his apartment in contemporary New York, only to be taken in by young, white neighbour Kiki. She fakes-up medical insurance where she works to get Soupspoon the cancer treatment he needs, and as his strength returns, the former bluesman begins to tape his memories of an early life in the south, of his love for a man called Robert Johnson.

Mosley’s book takes place mainly in the present, flashes back to the poor black life come intermittently; they never really get up a head of steam nor develop real characters. Johnson, as befits his legend, is held back and held back so far that he is ultimately as faded from the book as he is from the well-known photographs.

Mosley seems unsure how to balance his tale, and as a consequence the book is lop-sided, neither fish nor fowl. He has a violent, revenge sub-plot running alongside Soupspoon’s reminiscences and a more homely tale of a city underclass. On their own they might work, but cut together feel insubstantial, even though his handling of the contrasts between participants - black/white, young/old, men/women - is deft. He is as strong on detail as he is weak on structure.

And just occasionally he makes an ugly mistake of epic proportions. The gay man dying of AIDS is melodramatic, movie-of-the-week crass, and Mosley knows better.

Some of the writing is terrific - "But when RL tuned up you weren’t scared any more, because that man told you, ‘Yes it’s all true, so you better lap up the gravy while you can still lick’"; "Negroes had strong hearts and stronger backs. They carried the whole world on their shoulders and when they sighed it came blues" - but rarely does it evoke the music it speaks about to anyone not already familiar.

As good as his other books are, it’s hard to recommend this. Those Easy Rawlins thrillers are vivid creations, beautifully crafted as genre novels, but within a bigger, more telling picture about the lot of black America. RL’s Dream is not of the same class and makes one wonder if Mosley really needs the discipline of the crime novel. (His next is already announced as Easy Rawlins mystery Little Yellow Dog.) Improvising outside of those conventions, Bill Clinton’s favourite novelist has lost the tune.