Sister pact

My sister Rachael doesn't get out much, apparently because she is an actuary with two small children. Sometimes I ring up and say: Rach, let's go out tonight, there's a party/premiere/envelope opening we really must attend together.

If the timing is right she will say something like: Okay, but do you have any lipstick on you? Which is a bit like Paris Hilton's sister asking her whether she has any spare designer handbags. I told you she doesn't get out much.

We had one of our rare nights out together last week, at a drinks party hosted by a radio station. We ended up sharing the table with Radio Head, who took a bit of shine to her, on account of their having the maths thing in common. He came first in his class at probability, which meant nothing to me but impressed Rachael, who can add up big numbers in her head.

The very happily married Radio Head and the very happily married actuary chatted happily about managing Irish people's increasingly unrealistic pensions expectations. I don't know what it means, either - and, anyway, I was more interested in the mini bagel burgers. They hit it off by working out how long the other had to live. My sister's very attractive for an actuary.

After a few drinks and a bit more chat, Radio Head said he reckoned he had the measure of us siblings. If we were paintings, he said, then I was a Rothko, all colourful and warm and fuzzy at the edges. The sister was not amused. "If she is Rothko, then what does that make me?" she hissed, getting that black look in her eye, the one that will be familiar to my brothers' ex-girlfriends, whom she has cross-examined almost to death on occasion.

You are an Escher print, all straight lines and unusual architecture . . . "Oh great," said Rach, cutting him off. "She gets to be all colourful and blurry, and I get to be all black and white, with stairs that go nowhere. What are you trying to say?" I should have told Radio Head to leave well enough alone, but I was enjoying the unfolding drama. "Escher paintings are very beautiful," he said hopefully. Rachael's stern face was, appropriately enough, a picture.

There follows an example of how Radio Head's perceptive Escher/Rothko comparison plays out between my sister and me. Earlier that evening I had picked her up from her office in a taxi. She was wearing one of her sharp trouser suits, with a white T-shirt underneath. I was wearing sparkly black eyeshadow and a coleslaw-stained floaty dress and carrying my usual assortment of grubby carrier bags.

We were off to a wine tasting in a fancy hotel. I needed someone with a bit of gravitas to accompany me. In addition to being rather good at sums, she knows her Bordeaux from her elbow; I just know I like fizzy stuff, Mad Fish and a nice Sancerre. She is also good at persuading me not to eat my way through large containers of duck pâté just because, like Everest, they are there. She wasn't as successful with the big pile of melty Brie and crackers. Yum.

Later, in the Porter House, she talked business and people management with Radio Head while I quizzed a friend's American date - a pianist at the Liberace Museum, in Las Vegas, if you wouldn't be minding - about how he got into music. At which point everyone listened open-mouthed as Wes Winters - yes, that's his real name - described seeing Liberace on the telly at the age of five and teaching himself, for the next eight years, to play piano like Liberace.

Then Rachael came over all Rothko and asked if he had any Dean Martin in his repertoire. Being the pro that he is, Wes had a lot of Deano, a lot of Elvis and quite a bit of Judy Garland. If you have never had a sing-song led by someone who actually knows the words and sounds like the people who used to sing the songs, go to Las Vegas to meet Wes immediately, if not sooner.

It's only natural that there are times when Rachael would like a bit more of my Rothko and I could do with more of her Escher, but most of the time I am perfectly happy with the way we are. It means that when life gets a bit fuzzy I can ring her for advice on a contract I am supposed to sign or a tax form I am supposed to fill in. It means that when life gets a bit black and white she can rely on me to force her to put on make-up and try on stunning dresses in Barcelona boutiques.

That night, though, the lines between Escher and Rothko blurred beautifully as we sang our hearts out with the wonderful Wes. It's times like these when Rachael and I are a real work of art.