I was Theresa May's neighbour for almost ten years - in a manner of speaking, anyway. Her Maidenhead constituency bordered my Wycombe one when I was a Member of Parliament. So I had plenty of time in which to take a view of her. What struck me most was a characteristic that seems to be at her core. She was determined, immensely diligent, canny, slightly chilly - and solitary. Amidst a mass of extroverts - politics attracts showboaters - she was an introvert.

This morning, as she totters on the edge of ruin, I keep returning to that thought. "An issue with Theresa," a Cabinet Minister once told me, "is that she doesn't trust anyone." This is the key to her rise and fall.

That shyness has been a stubborn constant amidst the shifting story of Mrs May. She has had three main incarnations. Theresa May One was the original moderniser - warning Conservative members, as Party Chairman, that theirs was seen as "the Nasty Party". Theresa May Two was formed by a double development: by an adviser and an appointment.

The adviser was Nick Timothy. Many Tories are socially and economically liberal. They prize the individual. Mr Timothy is the opposite. He leans towards interventionism. Margaret Thatcher used to speak of "our people" - the workers set free by council house and share sales. Mr Timothy's people are the hard-toiling workers of his native West Midlands, attached to the NHS, ripped off by inflated energy bills, hostile to uncontrolled immigration. Mrs May's speeches and talk became markedly more collectivist.

The appointment was to the Home Office. The department's culture is shaped by institutional suspicion. It sees its mission as being to stop illegal migrants entering the country and terrorists from carrying out mass atrocities. Its defensive culture reinforced Mrs May's withdrawn persona. She became steelier, tougher - and even harder to read. The EU referendum result upended David Cameron from Downing Street and propelled her in to it, after Michael Gove effectively removed Boris Johnson from the consequent leadership election, and left her as the last woman standing.