This is a must-see and one of the best documentaries - and films - of this year.

It's funny, it's tense, it features two great performances from two actors and the director expertly creates a web of odd tension where you actually don't know what is happening for the majority of the run time.

After playing with our expectations, this turns out to be a very different sort of film.

The film may be flawed, but its message is not.