Last June, on a hot day in London - hot enough to remind me of Lahore - I got on the Tube and found myself in a crowded carriage with one empty seat. Nobody moved to take it, which seemed strange because several people were standing. Then I noticed the fellow in the next seat over. He was, I guessed, of Pakistani origin, with intense eyes, a prayer cap, a loose kurta, and the kind of moustache-less beard that tabloids associate with Muslim fundamentalists. He could have been my cousin.
Look at this racial profiling, I thought to myself. Here's this fellow, perfectly harmless, and everyone's staying clear like he's planning to kill them. And then they wonder why Muslims in Britain feel ostracised.
I took the seat, gave the fellow a smile that meant, "Hello there, brother, we're on the same side," and opened my copy of the Economist. And that would have been that.
Except that it wasn't, because once the doors slammed shut and the train jerked forward, he said, disconcertingly loudly, "Why do Arabs get all the credit?"
I wasn't sure what to make of his question, so I said, "Excuse me?"
He jabbed his finger at the cover of my magazine. It carried a photograph of Abu Musab al-Zarqawi, by reputation a particularly nasty Jordanian militant, killed a few days previously in Iraq.
"Why do Arabs," he said again, almost shouting, "get all the credit?"
I observed that he had earphones on, the small fit-in-your-ear iPod variety, and also that people had started staring at us.
"I'm not sure I know what you mean, friend," I said, forcing another smile on to my face. Then I added, "I'm from Pakistan myself."
I added this because I wanted to make sure he understood the connection between us. I also added it because he was acting a little odd and I thought that if he actually was a terrorist he might be less likely to blow himself to smithereens if he knew he was sitting next to another Muslim.
His eyes began to leap from me to the magazine, to the window, to me again. Over and over. It occurred to me that we were getting rather close to the first anniversary of the 7/7 bombings. Didn't terrorists have a thing about anniversaries?
"And where are you from?" I said, coaxingly. Distract him. Keep him talking. Establish a rapport.
"I'm in the security business. Get it? The security business. My own company. And I like music. I bought a system for £10,000."
OK, then. This fellow clearly wasn't flying on all four engines. And he was nervous. He was sweating like a Swede in the Sahara. And what was that? Yes, he had a bulge under his kurta. Like a money belt. A very, very large money belt.
Play for time. "I'm a bit of a music fanatic myself," I said. I winced inwardly at my unfortunate use of the word fanatic, then went on. "I have this old Carver power amp. Bought it way back in '93 or '94. Just the sweetest sound."
He took his earphones off, slowly, and glared at me. I watched his every move. I wasn't the only one. And I got the feeling that we had a few eavesdroppers as well. Like that woman reading Jamie Oliver upside-down.
Then he said, "I'm on medication, did you know that?"
"Er, no. Are you... all right now?"
"STOP TALKING TO ME!"
Now we had everyone's attention. "Sure. OK. Sorry."
He put his headphones on again. I observed him, James Bond-like, out of the corner of my eye. I wondered how he would trigger the explosives. Would he raise his arm, relying on a hidden detonator built into his sleeve? Or would he have to reach under his kurta and press a button on the bomb itself?
I readied myself for action. I ran kung-fu moves through my mind, super-slow, at Matrix special-effects speed. I would have to grab him, pin his arms to his side, and hold on while squealing like a schoolgirl for help.
He looked at his watch. So did I. Five o'clock. And not just five o'clock. Exactly, to the second, five o'clock. This was it.
The train started to slow. We were pulling into a station. My station. Just a few more moments. Maybe I would make it.
Nothing happened. We arrived, the doors opened, and he and I simultaneously rose and exited on to the platform. I stood and watched him walk away, wondering if I should say something. He was perhaps the most suspicious person I had ever seen in my life.
But remembering my own experience of "random" searches and multi-hour detentions at immigration lounges around the world, I thought of what might happen to the fellow if I mentioned him to the authorities. He would be stopped. He would act strangely. Even if he was completely innocent, which he probably was, he might well resist being questioned. And then, for no fault of his own, he might find himself under arrest.
I couldn't set in motion that sequence of events. So I did nothing, and I hoped I would not discover on the television later that evening that my inaction had made possible a slaughter.
Stepping into the open air, I found my friend, who was visiting me from Pakistan, and told him the story of what had just happened.
He laughed. "You're just paranoid, yaar," he said. "You've been living here too long."
Mohsin Hamid's novel 'The Reluctant Fundamentalist', will be published by Hamish Hamilton in March