Here is a section of the book's website:
Muhammad was an orphan. Spurned by his mother in his infancy and left in the care of a Bedouin couple, he had a loveless childhood. He then passed to the care of his grandfather and uncle who took pity on him and spoiled him. Not receiving love at a time he needed unconditional love and not receiving discipline when he needed to learn about boundaries, he developed narcissistic personality disorder, a trait that made him a megalomaniac bereft of conscience. He fantasized about unlimited power, expected praise and admiration, believed he was special, and expected others to believe him and go along with his ideas and plans. He took advantage of others, was jealous, yet believed others were jealous of him, and was extremely hurt when rejected, even killing those who deserted him. He lied and deceived, feeling entitled and justified in doing so. All these are traits of narcissistic personality disorder.
Thanks to another mental illness, temporal lobe epilepsy, the prophet of Islam had vivid hallucinations he interpreted as mystical and divine intimations. When he claimed he heard voices, saw angels and other ghostly entities, he was not lying. His problem was that he could not distinguish reality from fantasy.