Stephen Sackur talks to one of Britain's leading brain surgeons, Henry Marsh. Imagine you are a patient about to undergo brain surgery. If it goes well, it will save your life; if it goes wrong, you could end up paralysed or dead. Of course, you want to believe your surgeon is infallible, a superhero. But he is not; he is all too human just like you. That simple truth emerges from the extraordinarily honest writing of Dr Henry Marsh. He has given us rare insight into the mind of the doctor; is it reassuring or troubling?