Clint Eastwood's biopic of FBI boss J Edgar Hoover pads earnestly and quietly through a turbulent tale that encompasses the greater part of 20th century.

The script by Dustin Lance Black (Milk) works that most tired of biopic conventions, the subject at the end of their life dictating a memoir, but from that crafts a multi-strand mosaic that flips back and forth between various ongoing tales from numerous points in his life.

Being handed the role of repressed bisexual cross dressing law enforcement officer would normally be a green light to grandstand, but DiCaprio holds himself in.

Placed in the centre of a Scorsese barrage of light and sound he can often seem a bit lacking, but he's right at home in Eastwood's low key vision.

Of the three central performers – Naomi Watts as Hoover's loyal secretary Helen Gandy and Armie Hammer as his partner and presumed lover Clyde Tolson – who have to appear throughout the entire 53 years of the film's timeline, DiCaprio fares the best with the aging prosthetics.

Frustratingly, Hoover did a remarkable job of taking his secrets with him to the grave.

Nobody quite knows what dirt he had on everybody else, or quite what dirt he was hiding about himself. Such a void makes him an empty canvas for artists to paint their own obsessions onto but this film opts for studied neutrality.

Given the trashing Hoover's reputation has taken after his death, such an approach makes for a comparative sympathetic portrait; you get his side of the story.

However, viewers hoping for some kind of point will wait in vain. The film has more false endings than Return of the King. It keeps going in the hope of alighting on some culminating image but doesn't find it. It knows that this man's life says something important about America, but it doesn't know what it is.

J.EDGAR (15)

Director: Clint Eastwood.

Starring: Leonardo DiCaprio, Armie Hammer, Naomi Watts, Judi Dench, Josh Lucas and Stephen Root.

Length: 137 mins.

***