Initially kicking off his documentary about Lance Armstrong back in 2009 for his much heralded comeback after retiring his retirement, director Alex Gibney found himself in exactly the right place at exactly the right time. Armstrong, for years a people's champion and constantly on the receiving end of cheating-via-substance-abuse rumours, found himself in the centre of a focused, hounding operation to prove him a cheater once and for all.

Here, Gibney goes through most of Armstrong's life, flying through his early years and spending the majority of the film juxtaposing the 2009 Armstrong who is adamant he has never used performance enhancing drugs, with the post-Oprah interview 2013 Armstrong who has finally come clean about the fact he was far from clean when he won all of those races. There is something of a giddy thrill from watching just how good an actor Armstrong was, and how he finally had to crumble in the face of undeniable evidence.

There is also a lot of moral and ethical questions going on the in the background of The Armstrong Lie, such as if everyone in the race is cheating, doesn't that put everyone back on an even keel? And if Armstrong - a cancer survivor - used his position as a celebrity to raise hundreds of millions of dollars for cancer research and charities, then can the positive outcomes allow us to forgive him his negative actions? And when does the saturation effect of a rumour regarding a celebrity reach a point that it becomes a generally believed fact, with or without the proof to back it up?

Gibney is a prolific, hugely successful documentary director - being the guy behind the likes of Enron: The Smartest Guys In The Room, Taxi To The Dark Side, Mea Maxima Culpa: Silence In The House Of God and We Steal Secrets: The Story Of Wikileaks - knows how to get to the core of the subject matter, and reveals a nasty, dangerous side to Armstrong. Interviewing former teammates, doctors, race officials and journalists, we get a good luck at a man who has built his house of lies on the fairly solid foundations of wealth and fame, and who is not afraid to use all the goodwill he has garnered as a form of offense against anyone who might have the audacity to speak the truth about him.

At just over two hours, Gibney doesn't quite know when to call cut, over-emphasising some of his points while barely giving a sideways glance at others, and for anyone with a passing knowledge of the subject, The Armstrong Lie is far from revelatory, but it is highly insightful and very entertaining.