As well as investigating the difference/disease and nature/nurture issues, the book examines the different types of mental illness. Schizophrenia and depression are both mental illnesses, but are very different in their effects. Nettle considers whether we should think of a line with normality at one end and mental illness at the other - possibly splitting into two - or whether it's a case of depression and schizophrenia being two extremes with normality in the middle. The book goes on to look at the brain chemistry which is involved in these illnesses, and the varying successes of drug treatments
Later in the book Nettle goes into more details of the link between creativity and mental problems. He argues that evolution has selected for the benefits of creativity, and in particular sexual selection has led to the most imaginative individuals being the ones to reproduce, but in excess this trait may result in mental illness. However, I felt that there there wasn't as much about the links between 'the lunatic, the lover and the poet' as the cover would suggest. The book is aimed much more at those readers wanting to find out about mental illness rather than those wanting to find out about creativity.