We were given a topic to think about over the Christmas/New Year break. We were asked to write a story about a promise or a pledge. For a long time, I couldn't come up any ideas at all. But then I remembered a (probably apocryphal) story about a someone who promised free things to pensioners who turned up with their parents. Obviously he didn't really expect anybody to take advantage of the offer -- he just wanted the publicity. So I decided to write about that situation. Clearly I had to make. the premise of a pensioner with parents plausible so I did that by using a scenario that actually happened three times during my years at school. Problem solved. Then all I had to do was figure out how to make the promise interesting. Sex seemed like the best way of doing that. Everybody's interested in sex...

My 70th birthday party was a small, intimate affair. The only guests were my parents, and since we all live in the same house, it would have been very difficult for them to avoid the party even if they’d wanted to, which they didn’t! Fortunately we all like each other a lot and so it was no hardship for any of us to celebrate my birthday together.

My dad’s birthday is only a few days after mine, so as usual, we decided to have a combined 70th birthday party for me and 84th birthday for him, all on the same day. Mum is a couple of months younger than dad and they are both still very spry, if the sounds I hear coming from their bedroom are anything to go by.

If you do the arithmetic, you’ll realise that I was born when they were both only fourteen years old. Apparently it was the scandal of the school! The heat of the gossip practically burned the varnish off the desks and evaporated the ink out of the inkwells. Mum told me later that she and dad came under enormous pressure to have me adopted, but they presented a united front to their parents and other associated do-gooders and insisted on bringing me up themselves, so eventually everybody had to back down and let them have their way, though not without lots of dire muttering about how mum and dad were making a terrible mistake, they were ruining their lives, the relationship would never last… I’m sure that the whole family went to their graves still expecting mum and dad to split up any minute now and force the grandparents to have to bring me up. But seventy years later mum and dad are still together, still happy with each other’s company and showing no signs whatsoever of drifting apart.

"Perhaps we’ll get divorced after you die," dad said to me once. "I don’t think it’s fair for parents to separate while their children are still alive. You’d probably find it very traumatic and have to have expensive counselling sessions so as to come to terms with it. I wouldn’t wish that on anybody."

I think he might have been joking when he said that. I checked with mum, but she just smiled and backed him up so I remain none the wiser. Not that it matters. I won’t be here to see what they do after I die, so I don’t really care.

When I was little, the fact that my parents were only fourteen years older than me didn’t really register as a problem. For a small child, fourteen years is an eternity, and mum and dad seemed old and, presumably, wise to little me. Their age did give them some advantages – they won the egg and spoon race every year at my school’s parents’ sports day because they were so much younger than all the other parents.

But as the years passed and we all grew up, the age difference began to seem less and less important and for the last fifty years or so we’ve just been friends who happen to live together.

Dad gulped down the last of his champagne and checked his watch. "We ought to be leaving soon," he said. "We don’t want to miss the start of the film."

"Film?" asked mum.

"We’re all going to the cinema," said dad. "We’re going to see The 69 Steps."

"Don’t you mean The 39 Steps?" asked mum, sounding puzzled. "From the novel by John Buchan. It’s an Alfred Hitchcock film, I think."

"No," I explained. "This is a recent re-make of that old story. It’s a very pornographic adaptation, so they’ve renamed it as The 69 Steps."

"Why would I want to go to the cinema to see a pornographic movie?" asked mum. "I can watch all the pornography I want on the internet without having to leave the comfort of my own chair."

Dad and I looked at each other and made a silent agreement not to explore the implications of that observation. "The cinema has an advertising gimmick going on," explained dad. "If anybody who is 69 or older turns turns up accompanied by their parents, the whole family gets in free. Who can resist a bargain like that?"

"Clearly they aren’t expecting to have to honour the offer," I said. "Very few 69 year old people will have parents who are still alive. And those few parents who are still alive are probably in no fit state to be allowed out in public without extensive specialist supervision."

"I see," said mum thoughtfully. "So really the only people who will be able to take advantage of the offer are people like us."

"Why do you think I let you take me to your bed in the first place?" asked dad. "It was all just my cunning plan to get us free admission to the cinema seventy years later."

"How clever of you," said mum drily. "You always were very good at long range planning."

"So anyway," I said, "I thought it might be fun to take them up on their offer," I turned to dad. "Have you got all the necessary documentation?" I asked. "They aren’t going to believe us unless we can prove we’re telling the truth."

Dad patted his jacket pocket. "I’ve got your birth certificate," he said. "I’ve got your mum’s birth certificate and mine as well. I’ve got our marriage certificate and I’ve got some unbelievably cute photographs of you toddling around at our wedding with a helium balloon tied to your waist so that you wouldn't get lost in the crowds."

"Thanks dad," I said. "Though I’m not sure the photographs will help very much. You probably ought to take your passport as well, so that you can prove that you and mum really are the people listed as my parents on my birth certificate."

"I’ve got them in this pocket," said dad, patting his jacket on the other side.

That covered everything, so without further ado we piled into the car and drove to the cinema.

The queue seemed to stretch out forever. "I’ve not seen this many people waiting to get into a cinema for years," said mum. "Not since 1972 when I queued up to see Deep Throat."

Dad and I exchanged glances again. I was learning a lot of new things about mum tonight, though dad didn’t seem very surprised.

"Didn’t teach me anything I didn’t already know," said mum reminiscently, and dad went a bit scarlet and cleared his throat rather deeply…

The cinema manager was thrilled to see us. He examined our documentation in detail and then said, "Well, I must confess that I never thought anybody would take me up on my promise. But now that you are here, it will be great publicity. If you don’t mind, I’ll get in touch with the local newspaper and tell them about it. I expect they’ll come round to your house to take photographs."

"That’s fine," said dad. "Can we go and see the film now?"

"Of course," said the manager, and he personally showed us to our seats.

The film was really rather fun, if you like that sort of thing, which my mum clearly did. She had a great big smile plastered all over her face as we watched the hero, Richard Hannay, go up all sixty nine steps one by one. He kept having erotic encounters on every step and the higher he got the more imaginative they became. I’m fairly sure he cheated though. Unless I was missing something subtle, it seemed to me that step number fifty three was exactly the same as step number forty two except that everybody had their fingers crossed.

I heard the rustle of paper, and I glanced across at mum. By the light reflected from the screen I could see that she was busy taking copious notes. The tip of her tongue peeked out from the corner of her lips as she concentrated on her scribbling.

After sixty nine minutes the film came to an end. I thought that was a nice gimmick and I wondered if anyone else had noticed. "That was quite an eye-opener," said mum. "Lots of good suggestions to follow up on." She tucked her notes carefully into her handbag and as we walked towards the car, she linked arms with dad. "Come on you," she said. "We’ve got some homework to do." When we got to the car, mum pushed fifty dollars into my pocket and said, "Happy birthday, dear. Now, why don’t you make yourself scarce for a while. Go to the pub or something. Your dad and I have to do some, errr... studying."

They climbed into the car and I headed off by myself. "Don’t forget to cross your fingers," I called out to them. They waved cheerfully at me and drove away home.