I've been really poor the past few months. It's been really depressing, not in the least because my flat mates weren't talking to me because I was having trouble paying bills. I was starting to get really down, and then on Thursday I had an omen. I went for a long walk around Tooting to see if there were any jobs lying about, and as I walked I saw a road sign saying Recovery Street. Chuffed that I was on the road to recovery, I went home, confident everything was going to be fine. Sure enough, the next day I heard that a cheque had arrived for me in Ireland for 1000.

It arrived today and the first thing I did was buy a travelcard to go out to my sister's place in Richmond (something I was too poor to do yesterday). The trip out there increased my good mood – if you've ever lived in London, you'll know that having your trains all be precisely on time always cheers you up, on the rare occasions that it happens. I walked out to my sister's place, feeling like I'd turned some sort of karmic corner, and things were looking up. I got off the train, and outside the station there was a homeless guy under a blanket, with a beautiful white rat in his lap. It all felt a bit surreal.

On the way home, I was outside the Tesco in Richmond when I made eye contact with this girl. She was pretty, although only about 17. She looked a little like one of my flat mates actually – black hair, thin glasses, even wearing the same long black coat with a turquoise scarf. The eye contact was only for a second, and I didn't think much of it. Until she stopped and said, 'excuse me?' I stopped too and wheeled around to face her.

She began by saying, 'I'm sorry, but I need to ask you…' As a Londoner, these words instinctively make you want to keep walking, as briskly as possible. There's nothing that can be said after these words that I would ever want to listen to, and unless I already have some loose change I want to part with, there's nothing that's going to make me reach in my pockets. But I didn't walk away. There was something about her – she was dressed like my flat mate, had a quiet, polite voice, and seemed a bit upset. She carried on with, 'I know this is really rude. I've managed to get myself stuck in Richmond, and I don't have any money, and I really need to get back to Hendon and I know that this is really rude, but I'm really, really stuck.'

Behind her glasses, her eyes were welling up with tears. I found myself in a conflict – part of myself thought, 'wow, a poor teenage girl is lost in Richmond and having to beg'. But another, larger part of my brain was thinking 'London. Person on street asking for money. Fuck 'em.' In the end I compromised, mumbled something and reached for what change I had in my pocket. It was only about 90p. I dumped it into her hand and walked on.

Half way up the street, I was still thinking about it, and the more I thought about it, the worse I felt. This girl – lost, broke, scared. God knows how she'd ended up there, but she didn't seem like a street kid, and was probably at the end of her tether if she had to go around begging. I started feeling a bit guilty. In spite of myself, I am a great believer in omens and signs. My money arriving just as the bills and rent were looking unbearable was a definite sign, it really felt like I'd been given one last chance by some divine force. And here I was, with a real opportunity to actually help someone in need, and I'd walked away. I was close to the train station when I convinced myself that by ignoring her, I'd spat in the face of the cosmos, and that if I wanted my good luck to continue, I needed to try to share it with as many people as possible. So I did something I never did before.

I turned around, and went back to find her.

She was difficult to find. In fact, I had given up, and was walking back to the train station, when I saw her on the other side of the street, talking to an Asian guy in a suit. I watched him walk away without giving her anything and crossed over. 'Hi,' I said, 'have you had any luck?'

She stared at me for a second, not knowing what to say. So I carried on and said, 'look, I'm actually going to the train station right now. If you want to come along, I can get you a ticket to Hendon.'

In that exact moment, I realized my mistake. I had kind of thought that she might be grateful. I had worried that she might be scared, thinking I was some dodgy guy who might try to rob her or worse. What I didn't expect was a look of absolute disgust and disappointment. In my head, I slapped myself. She had absolutely no desire to go to Hendon. She just wanted the money.

'Um, are you sure?' she asked.

'Yeah. Uh, no problem. It's fine.' I couldn't bring myself to say I had changed my mind. Part of me was wondering if I was wrong, and didn't want to leave her stranded just cause she'd looked at me funny. Anyway, she looked so well dressed, and didn't seem like someone who'd scam change on the streets.

'That would be great,' she said without much conviction.

We walked to the train station in almost silence. I asked her how she had ended up in Richmond, and she said something vague about going to meet a friend in Kingston, but had been blown off by her and left alone. The walk wasn't very far. We got to the tube station in about 2 minutes. The beggar was still outside, but this time had an Alsatian on a leash, and no rat (rather bizarrely).

Inside, I couldn't see Hendon on the various buttons on the ticket machine. 'Um, y'know, it actually works out the same price to buy a travel ticket,' she said. I reached for the Travelcard zones 1,2,3,4 button. She stopped me, saying, 'no, it's 1,2,3,4,5 & 6'. As she reached across me, I saw the sleeve of her coat. It looked quite tattered.

'Of course it is,' I mumbled.

We walked down to the ticket barrier, where she said, 'um, I have to go to the ladies.' I wished her well and went for my train.

I waited, thinking either one of two things had happened. She was just a bit nervous about everything, seemed a bit off because she didn't know if I was going to suddenly attack her, and ran off cause she didn't want me following her home. Or, failing that, she was just hustling change on the street, saw an opportunity, got a travel card off me for the maximum amount possible and would attempt to hock it outside the station once she'd ditched me (selling travelcards on the street is quite common in London). Thing is, both theories seemed improbable. I got on my train, and was resigned to never knowing whether I had done a good deed or just been scammed.

Then I had an idea. I got the tube map from my pocket and searched for Hendon. Sure enough – there it was, safely nestled in Zone 4.

Still, I felt I'd learned an important lesson. If I had really wanted to be a Good Samaritan, I should have given it to the guy with the rat.