Writer/director Courtney Hunt has created a gripping and moving story so convincing it could be mistaken for a documentary.

The tale of a single mother trying to take care of her children seems commonplace in today’s society, but it is rare to see a film dedicated to the struggle.

Traditionally, stories of characters overcoming the odds to survive and find deliverance are written for and played by men, but Hunt realises there are few more emotive protagonists than a mother trying to provide for her children.

Ray Eddy and her two sons live in a tiny, rusted trailer on the subzero banks of the New York side of the St. Lawrence river, which divides the United States from Canada.

Her husband has run off to gamble away the money they had saved for a bigger trailer, her current trailer is not properly insulated, and she cannot get enough work so she has to feed her boys popcorn and fizzy drinks.

With her weathered face and foul mouth, Ray could have come across as hardened and insensitive, but Melissa Leo’s superb performance infuses the character with a sense of desperation that makes it impossible not to sympathise with her.

All the way through the film the audience is aware everything Ray does is for her children, so it is natural to root for her, even as she decides to break the law.

Her journey into crime begins when she sees her husband's car leave the parking lot of a bingo hall run by the Mohawk nation and gives chase.

The driver is Lila Littlewolf, played by the excellent Misty Upham, who is marginalized from her fellow Mohawks and has lost her baby to the mother of her recently deceased husband because she is too poor to care for her.

The two single mothers enter into an uneasy partnership, born from mutual desperation, smuggling illegal immigrants across the border in the boot of Ray's car.

Driving across the frozen river, terrified they will plummet into the water, the law will catch them, or the dodgy dealers they work for will kill them, Ray and Lila forge an unspoken bond.

But this is not Thelma and Louise. Hunt is not a sentimental storyteller.

The developing friendship between the two women is shown through their body language and facial expressions and the drama of each trip across the frozen river unfolds realistically rather than through manipulative fast-cuts or high-speed chases.

In the end, both women find a form of deliverance, but it is a lesser of two evils rather than a Hollywood happy ending.

But the realism makes Frozen River a powerful and deeply affecting experience.

Frozen River (15) is out July 17