The film makes a home in your brain and the only cure is to see it again.

A film with more than the usual spoiler issues. Talking about it in any detail feels akin to handing you a gift-wrapped present and saying, "I hope you like it -- It's a thriller about a diabolical secret experiment."

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

The storyline feels a little thin and moth-eaten in parts but this sequel is plenty of fun.