First Night: Venus and Serena, Toronto Film Festival

A surprise revelation at heart of this reticent yet insightful tale of two sisters

The film portrays Venus, left, as the protector, willing to defer to her younger sister

The directors Maiken Baird and Michelle Major followed the tennis superstars Venus Williams and Serena Williams throughout 2011 to make this insightful documentary about the famous siblings.

Starting with a potted history of the rise of the sisters, the documentary settles down in January 2011 with Serena being rushed to hospital suffering from blood clots and lung problems. In showing Serena looking bruised on a hospital trolley, the directors set their stall that this will not be just another puff piece.

With Venus now in her early 30s and prone to injury, the directors lucked out in that this would be a year of much frustration and downtime for the sisters.

Inside the home that the sisters share in Miami, the documentary shows Serena getting addicted to karaoke during her recovery. The girls come across, despite the tantrums and setbacks, as dedicated, friendly and supremely competitive.

One of the key figures in the Williams story is their father Richard, who saw tennis as a way to get his family out of Compton, a downtrodden area of Los Angeles. The sisters credit their tennis success to him, despite claims from one disgruntled coach.

In the past decade, gossip has surrounded their parents' divorce. Their mother Oracene Price advises any woman that gets with Richard to "run". In the most extraordinary moment of the film, Richard comes to practise with Serena and is accompanied by a young boy of around 10, who refers to Richard as dad. In a subsequent interview, Serena reveals she has no idea who the boy is.

As for romance, there is more openness from Serena than Venus. A statement that Serena plans to get married in November 2011 is not backed up by any appearance by a current beau and when Venus asks if she will then move out, Serena looks mortified and says she'll reconsider her plans. While no saucy revelations are disclosed, a great conversation between Serena and her hitting partner Sasa Bajin sees Serena claim that, despite having publicly dated Brett Ratner, she is only into black guys. Sasa quickly shoots this claim down.

The need for the girls to overcome racism in sport takes up a large portion of the documentary, backed by a hilarious interview with the comedian Chris Rock and out-takes of commentary by John Inverdale.

As for Venus, she is shown as the protector, an obsessive compulsive who ultimately is willing to defer to her sister. Not that she has much choice as Serena, with her 15 singles grand slam titles to Venus' seven, has long since proven herself to be the better tennis player.

The pair are Jehovah's Witnesses. Venus says that it is a big part of their life, but religion is surprisingly absent is this otherwise outstanding documentary.