In 1990, Peter Larson and his team found the largest, most complete Tyrannosaurus Rex ever found.
In 1990, Peter Larson and his team found the largest, most complete Tyrannosaurus Rex ever found. Dogwoof

When palaeontologist Peter Larson unearthed the world's largest, most complete fossil of a Tyrannosaurus Rex fossil, it was a career dream which turned into his worst nightmare.

The badlands of South Dakota are the mecca for fossil hunters, with some of the most spectacular finds uncovered here, including a sabretooth tiger skull and woolly mammoths.

This documentary charts the helter-skelter career of palaeontologist Peter Larson and his team from the Black Hills Institute of Geological Research, when they stumble upon the world's most complete T-rex.

However, finding the dinosaur is just the beginning of the story. It is also about fighting the might of the FBI, a custody battle, a grass roots protest, a complex legal case as well as a love story.

Director Todd Miller, in his first feature-length documentary, spins a gripping tale of how Hill City, with a population of 948, became involved in fighting the behemoth that is the US judicial system and the Federal Bureau of Investigation.

Strong emotion surrounds the finding of the T-rex, which they name Sue, after Sue Hendrickson, a palaeontologist working for the Black Hills Institute of Geological Research.

Locals of Hill City shed tears when speaking of the 65 million-year-old fossil. Larson is obsessed with the dinosaur and even his wife (who he met in a whirlwind romance during the 10-year saga), talks enviously of how the palaeontologist would spend time alone with Sue, and speak to her.

However, events spin out of control when the FBI seize Sue in a dispute over who was the rightful owner – whether it was Maurice Williams on whose land the dinosaur was found, the federal government, or the Black Hills Institute.

Extraordinarily, the court battle, which was the longest criminal trial in South Dakota state history, ended up with Larson convicted of two counts of customs violations, for which he served two years in federal prison.

The film charts his trajectory from a youthful and vibrant figure to a careworn, seemingly broken man.

One of the most poignant moments is Larson's account of his arrival in prison, when one of the warders reads over his papers, which basically says he is in prison because he didn't fill in the correct forms. "You must have seriously pissed someone off," says the guard.

Fortunately, Larson has his passion for fossils and dinosaurs to see him through the dark days of his incarceration. It could have turned him into a bitter man, but at the end of the film, he is back at work in the hills of South Dakota, still looking for dinosaur remains.

He might not have found another Sue, but since then he and his team have found three nearly complete skeletons of Triceratops in a site in Wyoming.

This David and Goliath story is an emotional rollercoaster, not only for Larson but also the people around him and a refusal to break the human spirit, even through adversity.

Dinosaur 13 is in UK cinemas from 15 August.