It was freezing on Brighton seafront, the numbing wind carrying a good dose of the sea’s brine. I could see the lights of the pier, twinkling up ahead. I pushed my frigid hands deep into my pockets and, head down, strode on. I was walking as fast as I could, having to will myself not to break into a run: I knew if I arrived at the police cordon breathless and sweaty it was bound to arouse suspicion, prompt unwelcome questions. Whatever happened, I needed to get in there unnoticed.

Get in, do what I had come here to do, and hopefully – there was absolutely no guarantee of this – make it out of the building again alive. I glanced at my watch. It was after one am already, but with all the adrenaline pumping through me it somehow didn’t feel like the middle of the night.

I spotted the hotel a long way off. It was unmissable: huge, like a giant wedding cake, tier upon tier, with elaborate cast-iron balconies running the length of its front on every floor. The whole thing was lit up by floodlights shining up from the semi-circular lawn in front of it: the rooms must have very good curtains or there was no way any of their guests would ever get any sleep. Its name was picked out across the lowest balcony in gold letters that must be almost as tall as I was: GRAND.

Outside it the road was blocked with bollards, and I could see uniformed policemen stopping cars driving along the seafront: I made sure to turn off the chilly promenade well before any of them could spot me, and instead headed inland, zig-zagging through the streets until I spotted the concrete bulk of an NCP car park looming up above the rooftops. If what I had been told was correct, the staff entrance was down the side of it, and barely guarded at all. My disguise should be enough to get me inside. If I was lucky. And I only needed to be lucky once.

There was an alleyway running along the edge of the multistorey, just as I had been told. A single crash barrier across it and a bored-looking policeman standing there. Deep breath; keep walking; stay as casual as possible. Try to look like I did this every day.

‘Morning!’ I said as I approached him, trying to keep my voice steady and holding the ID card I had been given out in front of me like a talisman. My heart was beating so fast and so loud I was surprised he couldn’t hear it in the still night air.

‘Cor, they work you lot nearly as hard as they work us, don’t they,’ he said cheerily, taking in the bow tie and crisp white shirt that made up my waiter’s outfit. He barely glanced at the card in my hand as he shifted the barrier aside to let me through. He had a ruddy, friendly face; quite handsome. Not so much older than I was. Probably had a family waiting for him back home. But I forced myself not to think about that right now.

‘No rest for the wicked!’ I quavered in a voice half an octave higher than my usual one, and I walked on.

A blast of warm air greeted me as I approached the shabby double doors at the end of the alleyway. Great extractor fan vents on the back of the building were pouring out heat and a thick fug of fatty meat smells. The back of the building could hardly be more different from the fancy frontage: the alley was lined with bins, pallets, broken-down cardboard boxes and empty cooking-oil cans. Two of the round drums separate from the rest served as the seats in a smoker’s area, judging by the dozens of cigarette butts scattered around them. Assuming the policeman’s eyes were still on me – there was sod all else to look at at this time of night – I tried hard not to break pace as I approached the doors, pushing them confidently and mouthing a silent thanks as they swung inwards. And I was in.

I found myself in a dingy hallway, the linoleum floor all but covered with overflowing wicker laundry baskets. On the right was a kitchen storeroom lined with wire shelves holding enormous cooking pots from floor to ceiling; on my left rose a bare flight of stairs. Somewhere up there, several floors above me, among hundreds of other sleeping people, right now, was Margaret Thatcher. And if I, Tommy Wildeblood, had got things right, then she, her entire cabinet, and God knows how many other supporters of her vicious disgrace of a government were all going to die tonight.