There is an egg-like object in my pocket. It was given to me by John Lennon. And it was given to him by ...

We were eating in some restaurant in New York City . Yoko was with us, so this was after their big break-up and reconciliation. Yoko was expecting their child, Sean, and John was excited - he was going to love this baby day and night, feed it, change it, teach it to talk, teach it to love music. He did all of that.

And he was going to watch it grow into adolescence, through the tumbles from bicycles and terrors of school-days, from reading to dating to college. He never got to do that.

John started talking about UFOs. He said he believed life existed on other planets, that it had visited us, that maybe it was observing us right now. He took me to a quieter, darker table, lit a cigarette and pointed its glowing tip at my face. "You believe in this stuff, right?" he asked me. "Well, you ain't effin' gonna believe this. About six months ago, I was asleep in my bed, with Yoko, at home, in the Dakota Building . And suddenly, I wasn't asleep. Because there was this blazing light round the door. It was shining through the cracks and the keyhole, like someone was out there with searchlights, or the apartment was on fire. That was what I thought - intruders, or fire. I leapt out of bed, and Yoko wasn't awake at all, she was lying there like a stone, and I pulled open the door. There were these four people out there."

"Fans?" I asked him.

"Well they didn't want my effin' autograph. They were, like, little. Bug-like. Big bug eyes and little bug mouths and they were scuttling at me like roaches." He broke off and stared at me. "I've told this to two other people, right? One was Yoko and she believes me. She says she doesn't understand it, but she knows I wouldn't lie to her. I told one other person, and she didn't believe me. She laughed it off, and then she said I must have been high. Well, I've been high, I mean right out of it, a lot of times, and I never saw anything on acid that was as weird as those effin' bugs, man. I was straight that night. I wasn't dreaming and I wasn't tripping. There were these creatures, like people but not like people, in my apartment."

"What did they do to you?"

Lennon swore again. "How do you know they did anything to me, man?"

"Because they must have come for a reason."

"You're right. They did something. But I don't know what it was. I tried to throw them out, but when I took a step towards them they kind of pushed me back. I mean, they didn't touch me. It was like they just willed me. Pushed me with willpower and telepathy."

"And then what?"

"I don't know. Something happened. Don't ask me what. Either I've forgotten, blocked it out, or they won't let me remember. But after a while they weren't there and I was just lying on the bed, next to Yoko, only I was on the covers. And she woke up and looked at me and asked what was wrong. I couldn't tell her at first. But I had this thing in my hands. They gave it to me."

"What was it?"

Lennon dug into his jeans pocket. "I've been carrying it round ever since, wanting to ask somebody the same question. You have it. Maybe you'll know."

I took the metal, egg-like object and turned it over in the dim light. It seemed solid and smooth, and I could make out no markings. "I've never seen anything like it."

"Keep it." John Lennon told me. "It's too weird for me. If it's my ticket to another planet, I don't want to go there."

In my career I have met two men whose lives have pivoted on war crimes. One was a Nazi scientist. The other was a Nazi-hunter.

I was introduced to Dr Werner von Braun by a Nasa astronaut, Captain Edgar Mitchell. Ed was the man who stood on the moon and tried to send back telepathic messages. I was escorted to Dr von Braun's office, where he had masterminded the US space program, and while he held his gold ring in his fist, I bent it psychically. "I have no scientific explanation for this phenomena," he remarked.

I was not aware until later that von Braun had also designed the V1 and V2 flying bombs which killed thousands during the Second World War. When Germany was defeated, his team was very close to creating atomic weapons. He had worked enthusiastically for the Führer, and I believe he deserved to stand trial - if not for his scientific work, which had murderous intent, then for his use of Jewish slave labour.

A dozen years later I met Simon Wiesenthal. He was obsessive about tracking down Nazis. His focus and concentration were inspiring, and his genuine humility shamed me - he really had no interest in fame, recognition or money. The encounter forced me to look at myself and ask which was more like myself - the man who demanded success at any price or the man who sacrificed everything to obey his conscience. I didn't like my answer. It was a major turning point in my life.