Blood's a Rover, By James Ellroy

A master crime novelist concludes his epic trilogy

There comes a point in this third and final instalment of the Underworld USA trilogy, James Ellroy's epic trawl through America's dark heart, when you want the ride to stop so you can get off. But you can't. It's so compelling that you have to see it through to the end. After which you can breathe fresh air again and look into the light while your stomach settles. Finishing it is like waking from a nightmare. The adult kind: fascinating despite its gruesomeness.

In the previous two instalments of his trilogy – 1995's American Tabloid and 2001's The Cold Six Thousand – Ellroy showed his readers what might have been going on beneath the rocks of American history between 1958 and 1968. By the time Blood's a Rover begins, John Kennedy is five years dead and his brother Bobby and the civil-rights leader Martin Luther King have just met with their assassins. So we join with those who plotted and carried out these killings, through to 1972. On the way, Tricky Richard Nixon is elected president, the FBI's notorious lifetime chief J Edgar Hoover is declining physically and mentally, black militancy is plunged into recrimination and criminality, and the insane movie mogul Howard Hughes sits receiving blood transfusions in a sterilised eyrie while plotting to buy up Las Vegas. Castro hovers in the background.

It's a heady brew, and has the same effect as the voodoo cocktails the main characters down while visiting Dominica's neighbour, Haiti – it induces a paranoiac dreamlike state.

Throw in the KKK, corrupt cops and Ellroy's trademark nastiness and violence and you have a convoluted tale that mixes fact with fiction (real-life characters such as the boxer Sonny Liston and the former teen actor Sal Mineo appear) and results in a flawed tour de force about the battle for America's soul. It is, as Ellroy has stated, bad juju.

The story hinges on an emerald heist with which the book opens. The search for the emeralds hooks in FBI Enforcer Dwight Holly; a former LAPD cop and "coon-killer" (forgive the language but Ellroy's unflinching style is not for the politically correct or faint of heart), Wayne Tedrow Jr; and rookie right-wing thug and Peeping Tom Don Crutchfield, also known as Dipshit. Ellroy also introduces a redemptive theme, with the characters crossing the political divide as they try to come to terms and make amends through violence for the violent and evil deeds they have done. There are strong women and unlikely alliances, there is treachery and betrayal.

Ellroy's trademark staccato style helps with the nightmare quality of the story. His technique of using "document inserts" – fictionalised FBI files, character journals and top-secret recorded transcripts between Nixon, Hoover and Holly – lend the book a historical feel. This is abetted by the author's complete grasp of the era's culture, politics, language and discourse. But there is a problem in making Blood's a Rover a quasi- historical narrative: the characters are ill-drawn, so much so that often it's difficult to know who's who. Apart from their politics and willingness to commit acts of violence, there is little to them and little to distinguish them. This, coupled with the frenetic nature of the prose, creates a headlong rush into confusion.

That shouldn't take away from Ellroy's achievement. The Underworld USA trilogy is a monumental work of fiction, his style is unique and compelling, and his theories of what lies behind the great unresolved events of America's noir history are utterly believable. He has said that he wants to be the greatest crime writer who ever lived. He is certainly one of the most original and daring writers alive. He's a sort of godfather – in the mafia sense – of American letters. He sits there perched on a rooftop like a dark, brooding and knowing angel.