The film uncovers the truth about how you really make decisions. Every day you make thousands of decisions, big and small, and behind all them is a powerful battle in your mind, pitting intuition against logic. This conflict affects every aspect of your life - from what you eat to what you believe, and especially to how you spend your money. And it turns out that the intuitive part of your mind is a lot more powerful than you may realise.

Horizon investigates the idea that the best way to lose weight successfully is a personalised approach, diets tailored to our individual biology and psychology. In a groundbreaking experiment, Dr Chris van Tulleken and Tanya Byron join a team of experts to put 75 overweight volunteers on diets designed to tackle the specific reasons why they eat too much. The volunteers are put through a series of tests at a residential clinic to understand how their genes, hormones and psychology influence their eating behaviour. They are then put on the diets the experts believe are best suited to them. Can science succeed where other diets have failed?

Dr Michael Mosley traces the sinister ways the experimental psychology has used to try to control our minds. He finds that the pursuit of mind control has led to some truly horrific experiments and left many casualties in its wake. Extraordinary archive captures what happened - scientists systematically change the behaviour of children; law abiding citizens give fatal electric shocks; a gay man has electrodes implanted in his head in an attempt to turn his sexuality. Michael takes a hallucinogenic drug as part of a controlled experiment to try to understand how its mind-bending properties can change the brain. This is a scientific journey goes to the very heart of what we hold most dear - our free will, and our ability to control our own destiny.

We now know that the brain - the organ that more than any other makes us human - is one of the wonders of the universe, and yet until the 17th century it was barely studied. The twin sciences of brain anatomy and psychology have offered different visions of who we are. Now these sciences are coming together and in the process have revealed some surprising and uncomfortable truths about what really shapes our thoughts, feelings and desires. And the search to understand how our brains work has also revealed that we are all - whether we realise it or not - carrying out science from the moment we are born.

Episode three explores the mind of one of the most fanatical of all Nazis and the insight that gives into the psychology of dictatorship. Hess is brought to Nuremberg from the UK where he had flown 4 years earlier much to the bemusement of the British. Overy explains that they must have quickly realised he was not normal. In the intervening time Hess’s mental state has further deteriorated and when interviewed by Chief Interrogator Colonel John Amen proclaims amnesia. Chief Interpreter Richard Sonnenfeldt explains that they brought in Göring to confront Hess but that he too failed to make an impression.
Psychopathologist Prof. Edgar Jones proposes Hess’s behaviour patterns may be his way of escaping reality as he is forced to face the extent of the atrocities and choose between accepting his part of the blame or forsaking his Führer. However, as history Professor Robert Gellatel explains it is difficult to construct a case against Hess as he was imprisoned in England when the worst of the atrocities were carried out so British Prosecutor Mervyn Griffith-Jones must argue a conspiracy charge linking the pre-1939 persecutions to the post-1939 atrocities and a crimes against peace charge proving the flight to Scotland was merely a ruse.

Moral psychology isn't always an easy thing to study. Experiments that actually puts people in what feels like a real scenario may get realistic results, but researchers must always balance the benefits of what we could learn with the safety and well-being of the people they study. Often what we learn from moral psychology experiments doesn't make humans look good.
We are imperfect creatures. But the more we learn about why and how we make the moral choices that we do, the better we'll be able to tackle difficult questions in the future.