The law is an ass and the people who administer it bigger asses in David Dobkin's courtroom drama about an estranged family reunited under the testing conditions of a murder trial.

The Judge takes its sweet time going through the legal motions, grafting on a superfluous romantic subplot to the revelations in the dock.

Thankfully, lead actors Robert Downey Jr and Robert Duvall sink their teeth into their broadly sketched characters and energise the dysfunctional father-son relationship that provides the film with its conflict and heart-tugging emotion.

Both men relish the verbal sparring, galvanized by screen chemistry that convinces us they are chips from the same unmovable block.

The lead role of a smarmy big city lawyer, who proudly proclaims, "Innocent people can't afford me", is a snug fit for Downey Jr.

Like Tony Stark in the Iron Man films, this slick operator has arrogance and wise-cracks to spare, yet, beneath the impeccably tailored suits and designer shades, there beats the fragile heart of a man terrified of losing the people he loves.

As the lead prosecutor of the murder trial sagely observes, "You're a bully with a big bag of tricks."

The legal eagle in question is Hank Palmer (Downey Jr), who helps his wealthy clients to escape the State of Illinois' prosecutorial clutches.

During one trial, Hank learns that his mother has passed away.

He ventures back to his hometown, which he abandoned 20 years ago, and tentatively rebuilds bridges with his two brothers, Glen (Vincent D'Onofrio) and Dale (Jeremy Strong), and father Joseph (Robert Duvall), who has been the community's venerable judge for 42 years.

His mood brightens when he learns that old flame Samantha (Vera Farmiga) owns the local bar.

As Hank prepares to fly back to Chicago, Joseph is arrested for killing a scoundrel who passed through his court.

Special prosecutor Dwight Dickham (Billy Bob Thornton) is drafted in to secure a conviction and Joseph chooses local defender CP Kennedy (Dax Shepard) rather than his son to represent him.

"Your honour, I'm going to fight like a badger for you," pledges Kennedy, whose inexperience in front of presiding Judge Warren (Ken Howard) convinces Hank that he needs to take charge of the case.

The Judge plays out the gradual role reversal of parents and children as caregivers in the rarefied surroundings of a wood-panelled courtroom.

Downey Jr and Duvall are both excellent and D'Onofrio and Strong offer sterling support as siblings in crisis.

Unfortunately, Farmiga is short-changed as the token love interest, who gives Hank a flimsy reason to stay in town.

Nick Schenk and Bill Dubuque's script doesn't conceal any narrative aces up its sleeve but does play fair, methodically resolving issues within the Palmer family as the court case reaches a suitably tense resolution.