More people wore masks on the train now than went bare-faced. A couple of businessmen even had oxygen masks. It was scary how fast people's perceptions changed. Only four weeks ago no-one wore a mask, now you got dirty looks if you dared breathe out in people's company. Never mind that the flimsy cotton did nothing to prevent infection. Last night there was a news item about a man being beaten by a crowd for the sin of sneezing on a bus. That was the real disease; not the death caused by the virus, but the madness with which it infects the public psyche.

Three percent were showing symptoms. Three percent of the world were praying they had a cold, but deep down knew they were going to die inside three months. Maybe another eight percent were infected, but were still incubating the disease, breeding the virus inside their bodies and expelling it into the air for a year or more.

I played a morbid game of statistics with my fellow passengers. You're dead, you're infected, so are you. That entire row are clean, but for how long? Is some viral advance guard even now skirting that useless nose cloth, setting up a beachhead in the semi-permeable membranes of your nose?

What would it be like, I wondered, to be the last man on earth? Pretty disgusting, probably. It wouldn't be the loneliness that got to you, it would be the stench of six billion rotting corpses.

The suicide rates were up. Who wanted to take three months to die a slow, painful death? On the other hand, church attendance was up too. You either saw the inevitability of the plague, and concluded there was no god, or you saw it as His displeasure at man's waywardness, thanked Him for sparing you (so far) and condemned the sufferers as the sinners they obviously were. I was neutral on the subject, though I knew for a certainty there was a devil.

No-one was making comedies any more. The box office was full of action heroes, stories of people taking on impossible odds and beating them, decisively. People didn't want to hear a story about how, with all our science and technology, we were helpless in the face of an infection. No triumph of good over evil, no victory. No inoculation, no cure, no hope. A cast of millions. No sequel planned.

People were working furiously for a cure, but there would be none. I knew, more than anyone else. It was, after all, my job: preventative anti-viral technologist. We thought we were onto a winner, splicing genes with the casual arrogance of a science that knew better than God. Ha! Maybe I did believe in Him after all. That would be one hell of a job appraisal, hauled up in front of the ultimate Boss to explain why I screwed up his pet project.

I'm not a bad person. How many people think they are? Even serial killers think they are doing the Lord's work. But I wanted to help. That's why I studied medicine in the first place. A couple of my colleagues joined worthy organisations like Medecins San Frontieres and the WHO. Deep down I was jealous of them; so noble, so selfless. I told myself that I could contribute to the good of humanity and still make a good living at the same time. Medical research for a large pharmaceutical was just as noble, but better paid.

Maybe I had visions of curing cancer, inoculating against HIV, being lauded for saving mankind from the death sentence of heart disease. Maybe, but there's not that much money in it. You want to know where the money is? Curing something that eighty percent or more of rich people get. Forget heart disease. If you stuff yourself with red meat and processed, sugar-filled crap, no drug is going to help you. Forget HIV, because the main market for a cure is third-world Africa, and how much money do they have?

So here I am, the saviour of mankind, the beneficent scientist that gave you (pause for trumpet fanfare) the cure for the common cold. (Waits for applause. Silence.)

Hey, don't knock it. Do you know how difficult that is? How many colds have you had? Me, I've had one every winter of my adult life, I think. The reason we keep getting colds is the little beggars keep mutating. Every time you catch a cold, it's a new variant, taking over a slightly different link in your DNA chain. Just creating a treatment that targets one form of pathogen without killing the host is difficult enough, but to create a generic cure? That's the Holy Grail. And I did it! I came up with a cure for the common cold.

Well, almost a cure for the common cold. It worked in the computer models. It worked in the Petri dishes. We tested it on animals, with perfect results. God forgive me, I was so full of myself. I saw myself doing the rounds of chat shows, becoming a celebrity boffin, like Stephen Hawking, but sexier. I wrote the Nobel Prize acceptance speech in my head. It was all going to be so Rock and Roll.

Who knew? Who would have thought that would lead me to heading up the principal research team charged with curing the virus that could wipe out humanity? The common cold, the Plague. Not exactly in the same league, right?

Wrong! It was exactly the same league. At first we didn't know, we didn't connect the dots. People thought it was bird flu, or the Black Death, or even some CIA plot that had run away from them. There was that country, God, I'm ashamed I can't remember the name, even with so many dead. You know, that one in Africa, that executed and burned any sufferers. How can you conceive of a situation where to cough is a capital offence? They closed their borders to keep themselves pure. Except an air-borne virus doesn't respect international borders or quarantine regulations. Millions dead, but such a small drop compared to the rest of the world, I can't even remember the name of the country.

Governments failed us. Science failed us. Even religion failed us. Ironic, isn't it? The only viable hope for mankind is me, sitting on this commuter train, and I am hopeless. Even if we find a cure, even if we can stop the spread, what hope is there for me?

I used to be full of hope. I believed in what we, no, what I had achieved. Yes, I had a big research team, but it was always my ego that drove it, so it's me that has to take the blame. It was me that, against objections, took part in the first human trial. It was my DNA that took the mutated virus with the specially-engineered gene sequence. And while it worked perfectly on the other volunteers, it was my DNA that went rogue, that started to produce the new cold virus. And a year later, when the Plague started to appear, it was my co-workers and friends that were amongst the first to die.

And to show what a sick sense of humour God has, once it had incubated in me, it left me whole. I'm forever clear of it. Every day I donate blood samples, skin samples, hair samples, in the hope that some clue in my DNA will stand up and shout, "Here! I'm the answer!" Every day I ride the train in the sure and certain knowledge that I don't need a face mask.

And the best thing? Two years now, and not a single cold.

Lucky me: the saviour of mankind.