In Mexico City, Trotsky was murdered. The details are notorious. The disciple who was really a Stalinist agent; the blast-proof steel doors, which opened to welcome the assassin; the ice pick, suddenly produced from a raincoat; the weight, post mortem, of the great man’s brain. I heard the story first from a follower.

‘Did you know that after his death they weighed his brain? It was vast. It weighed three pounds.’

I remember the awe in the voice of this normally cynical man. I had presumed that now, as research had revealed that brain size and weight are unrelated to intelligence, the myth of Trotsky’s brain had begun to die. But it takes more than facts to destroy a myth. Something of my friend’s awe remains with me still. It became my obsession to visit the house of Trotsky, where this vast brain had fed and grumbled and snored.