A plus one for business dinners, galas and private views

What separates a good plus one from a merely decorative one is preparation. When you write, tell the desk what the occasion is, where it takes place, what the invitation says about dress and what name and context you plan to give her. Say who will be present and anything best left unmentioned. She arrives knowing the shape of the evening, able to talk to the guest on her left as easily as to you, and alert to the moments when she should step aside so that a business conversation can happen without her.

A first name and a simple context work best: a friend, someone you invited for the evening. Nobody needs an elaborate story, and she will never embroider or contradict yours. If a colleague asks what she does, she has a practised, pleasant way of turning the question back towards them, which most people find flattering rather than evasive.

The museum quarter hosts evenings few other parts of London can match. Dinners are laid beneath the suspended whale skeleton in the Natural History Museum's Hintze Hall, receptions spill into the garden courtyard of the V&A, and gala nights at the Royal Albert Hall draw black tie crowds along Kensington Gore. Further west, the Design Museum, halfway along Kensington High Street, and the halls at Olympia host launches and industry dinners. Each has its own rhythm of arrivals, speeches and departures, and the briefing is the place to describe it.

The desk passes the dress code on word for word, though a few west London conventions are worth knowing.

A professional occasion carries different sensitivities from a private evening, and the desk plans for them. She takes no photographs of the event, posts nothing about it and never hands out or collects business contacts. Payments show only a neutral reference on your statement. If you would rather arrive separately and meet inside, or leave the venue at different times, say so in the briefing and it becomes part of the plan.

Formal evenings rarely finish on schedule. Speeches overrun, a conversation at the bar turns useful, a colleague suggests a last drink. Build a little margin into the booked length if you can. Should the night then carry on and her diary has room, a quick message to the desk before the hours run out extends it, with the extra paid alongside the balance.

Samanta has a performer's composure and quietly notes the design of every room she enters. Karolina can talk about the building you are standing in more interestingly than most of the guests, then fall silent at exactly the right moment. Violetta wears evening black and gold as though it were daywear, and her dry wit suits a long table. Margo follows the art world closely, which makes her ideal company at a private view in Holland Park or Kensington. Samanta, Karolina and Violetta all hang in the statuesque room of the collection.