Secret life of a private eye: The glitz, the glamour, the unconventional use of coffee cups...

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Fifteen years ago, I had an epiphany. I'd hit 30, three decades that culminated in my being a teacher and a single mum, living in Bexleyheath, south-east London. Yes, I had the school holidays, but call me flighty, I wanted more. If I could do anything, anything, what would it be? And let's face it, it had to be something outré, otherwise I'd be wearing that single-mum tabard for the rest of my life.

In an ideal world, I'd have had the time and brains to further my education – medicine, psychology, archaeology, quantum mechanics. That would have prepared me better for my pre-midlife crisis, given me avenues. What I had instead was a degree in geography – but one significant advantage over twentysomethings and the pubescent: I was born in the 1970s and grew up on a televisual diet of detective shows.

Lots of the TV detectives were women; glamorous ones with great hair and drink problems – Christine Cagney, Pepper Anderson, Charlie's Angels – their every move accompanied by jazz fusion that always felt thoroughly me. And over the years, I'd always felt privileged when other people confided in me. I'm not a gossip, quite the opposite – but the truth of the matter is, I like to know the ins and outs of a duck's arse. In a nice way.

So I decided to become a private investigator. My son, six, thought I was impossibly cool; among his friends, my street cred was off the chart. My sixtysomething parents knew better than to question my sanity. I have a spontaneous and stubborn streak; the one thing they did know was that, even if it was bonkers, I'd give it my all.

PIs tend to be mercenary, cold – it doesn't mean they're not good, it just means they're ex-soldiers/security guards/wannabe MI5 types, who are mostly men. I'd be a PI with a heart – you might see them on TV, but nobody has ever actually met one, which makes it a brilliant USP. I could bring a smidgeon of compassion to a job in which, fundamentally, you juggle with a stranger's emotions.

So that was all well and good. But how would I actually become a bona fide PI?

Turns out, it's not that complicated. I did an online course. At the end, I received a diploma. That diploma is meaningless – I basically paid £400 to a bloke to be given the industry secrets. The legal ones, that is (such as get the bill payer's permission before installing spyware, otherwise it's electricity theft). The illegal ones, you have to learn on your own (certain pen-pushers with useful information at their fingertips are worth their weight in cheeky fifties).

Then, when you come to set up your own firm, choose a harmless-looking name, one that could be mistaken for a market-research company or legal firm, so nobody blinks an eye when it turns up on a bank statement. If you can't do it yourself, get a friend to make you a website; research similar sites and copy what they say – in your own words, otherwise that's plagiarism.

The reality of most PI firms is that you're a one-person band who works from home, and sometimes out of the back of a Renault Kangoo (custom-tweaked, of course – you need to drill a few holes in the bodywork through which to poke pinhole cameras). Pretend you have an office full of personnel – give them names, set up email accounts. (Should you actually need extra manpower, you call your dad or a bestie.) Pay for your site to sit at the top of the search listings – that makes you look successful – even if it's for an hour a day. And get an 0800 number – that helps you look not needy. And if a case is beyond you, outsource it to a better-qualified PI and take a cut.

I remember my first day on the job, looking at my colour-coded folders in the corner of the sitting room, empty, but their spines alluding to exciting times ahead – Bigamy, Bounty Hunting, Corporate Espionage, DNA tests. All my gel pens had their lids on. An unopened ream of photographic paper sat by one shiny printer that had four functions. A Shewee lay in my handbag (for long stakeouts). Upstairs, I had hairpieces, glasses, dowdy clothes – the best way to disguise yourself being to make yourself plain and asexual, which is depressing yet liberating; and for the times I'd need to stand out – to attract male attention, say – you go designer. My spare bedroom was like the changing room from Mr Ben.

I was petrified when my website went live. Society's seedy underbelly was entirely new to me. I'd never met a real-life PI. I had, however, read a lot of Raymond Chandler. My first case arrived within the day, though I'm pretty sure my dad asked a favour of a friend. It was a missing person. All I had: a name and past address. The target hadn't been seen in two years. Suspicious. I looked at 192.com. He'd moved house. I solved the case within a minute. Eighty quid banked.

For a few days, it went quiet. I spent the time learning how to use the printer, swotting up on CIA surveillance techniques, and fending calls from local radio stations. They wanted me to partake in a discussion on the exploitative nature of private investigation. I was in no position to have an opinion either way. There were also a lot of "Welcome to the neighbourhood" calls from other PIs, checking me out, offering a bit of badly paid work, sneering, because, as a woman, they thought I was just playing at it.

And they were right, I was just playing at it – until job number two. It was straight out of Lovejoy – a messy heap of fraud, love and antiques theft. An elderly lady had fallen in love with a gardener. Both widowed, they were engaged to be married. Small but expensive possessions were going missing, and a relative of hers asked that I carry out a background check.

It always starts with Google. I'd ascertained that he was originally from the other end of the country, so when a man of the same name appeared in a local newspaper extract, I commissioned a search of the paper's archives. The gardener was part of an antiques gang and had spent the previous 20 years in and out of prison. I found he still had an address in Scotland, so hired a Scottish PI to visit the house. There he interviewed the occupant, the gardener's wife, who was alive and kicking – and spitting feathers because her husband had gone to the shops five years before and never come back.

The case was a roaring success. By which I mean the truth was outed. And so we come to the major downside of PI work: sometimes you are the bearer of bad news. Hearts get broken.

A Canadian woman called a few months later and asked that I do a background check on her British fiancé. He was due to move to Vancouver in just 10 days, but she'd received a text message from him – one that made her suspicious. A few basic searches confirmed her fears. The husband-to-be was coaching football at two schools in different counties. At each, he was the father of a pupil. The school websites had different mobile numbers for contact in an emergency. I carried out public-record checks, discovered three marriage certificates and no divorce papers. Estranged from wife number one, this woman's fiancé was already juggling two wives and six children.

Even when I provided the client with the certificates, mobile-phone numbers and title deeds of the houses he owned with his wives, he still professed to be innocent. I found that hard, telling someone their lover is not just a bastard but has a serious personality disorder.

Sending DVD evidence of an unfaithful partner to a client is another nasty prospect – but following cheating spouses is a mainstay of the job. When I caught them, I'd experience nausea imagining the client watching footage of their partner kissing someone else, or rushing arm-in-arm from a cab into a hotel. I spent a lot of time sitting in hotel foyers. But eventually I came to a firm conclusion: in the long run it's best to be in a relationship where both partners hold dear the principle of truth. And if you're so ruined that you need the help of someone like me, then better to have me.

Surprisingly, the outcome of most infidelity cases is positive for the client. There was one guy who disappeared to the pub every night. His wife said he was having an affair with the waitress. I posed as a barfly and watched from another stool for a good few nights. He wasn't having an affair with anybody. He was a loner who, when finally we had a fleeting chat, told me his wife was bonkers. I felt sorry for him. He's up to nothing at all, I reported back; to which I remember her being royally disappointed, then asking for her money back.

My favourite type of case was finding missing people, mostly biological parents or children. I received thank-you cards to my PO Box. PIs never get thank-you cards. Maybe I was lucky, maybe the lost family members I looked for wanted to be found, as I used the normal missing-people roots: electoral-roll software, the Land Registry, Companies House and public records. Genealogy is a fantastic tool; as are friends who are administrators in all the usual useful places.

There were also a few glamorous jobs. The Langham Hotel, London. I was dressed to the nines – no scrimping: you just put the price of your outfit and accessories on the bill. Especially when you land a job like this one – the target was a Russian oligarch. The client, his wife, didn't trust him. I watched him from a stool at the bar, a pinhole camera in my clutch pointed directly at him, checking out his counter-surveillance, wondering if they'd clocked me. You spend a lot of time, in the big cases, working out their security; they're as invisible as secret shoppers unless you know what to look for (placed in a pattern, avoiding eye contact at all costs).

Then, quite unexpectedly, George Clooney sat beside me. Champagne and hors d'oeuvres were placed in front of him. I forgot where I was and, after a while, asked if I could have his finger snacks, as he wasn't eating them and they were 20 quid a pop. In my own mind, George thought I was delightful. When Clooney's old friend Rande Gerber, Mr Cindy Crawford, rocked up and commented on how beautiful the bar was, George turned and looked me straight in the eye. "It's a mighty fine-looking bar," he said. I giggled like a fool. Then legged it, because the oligarch had left God knows how long before.

After about eight years, I brought it all to a close. Why? Because, unlike the 1970s cop shows, cases are very often not that exciting. Surveillance can be soul-destroying when nothing's happening – sitting outside a house or office for days, sometimes weeks on end, thinking of all the things you could be doing. There's also following people by car – I'm a 10-to-two driver, who prefers not exceeding speed limits; pissing in coffee cups, that's always a mini-disaster; and having no one to talk to, that's tough.

And before I knew it I'd hit 40 and all I knew was that the past four decades had culminated in my being a teacher-turned-private investigator. But if I could do anything, anything, what would it be? Especially when I had everything I needed: a kick-arse job, on paper, at least. Well, I was all right at writing, and being a PI was a kick-arse job, most especially on paper…

'The Last Honeytrap' by Louise Lee (£7.99, Headline) is out now