The best documentaries inform and provide insight into a subject, but when they also provoke moral outrage they can have a genuine, lasting impact on the viewer. A hit at the Sundance festival, director Dylan Mohan Gray's film chronicles how western pharmaceutical companies and governments blocked access to low-cost Aids drugs for populations in the developing world from the mid-1990s onwards. It will come as no surprise that for multinational drug companies it's all about making money. But Gray's incisive and damning examination of how these institutions made use of draconian patent laws to maximise their profits at the expense of the lives of millions is an enraging experience. It's not a documentary that tries to be showy - it contains the genre's standard components of talking heads, newspaper headlines and statistics. However, thanks to the testimonies of unsung heroes such as South African activist Zackie Achmat and Ugandan doctor Peter Mugyenyi, who defied the laws to try to save his patients ("The drugs are where the disease is not,"), the film is utterly absorbing and impossible to forget.