Calling hours: a companion sent to your hotel or house in W1, at any hour of the night or day

Most calls land a few minutes' walk from Berkeley Square, which is why so few of them run late. The May Fair Hotel occupies the corner of Stratton Street at the square's southern end; The Chesterfield is a minute west on Charles Street; Flemings and the Mayfair Townhouse share Half Moon Street, a little nearer Green Park. Brown's, on Albemarle Street, is closer than most visitors expect.

Westward, the grander addresses of Park Lane look across Hyde Park: The Dorchester with 45 Park Lane beside it, then Hamilton Place, where the Four Seasons and the InterContinental look towards the arch at Hyde Park Corner. Anywhere in W1 the wait after Cressida's confirmation is usually under an hour, and a call agreed in the afternoon for later that evening arrives at the minute you chose.

Before your companion sets out, Cressida asks once for the name the room is reserved under and the room number; at a private address she asks for the street and house number instead. The question protects her and reassures you, it stays in the thread where you answered it, and nobody asks it a second time. The booking page lays out the rest of the exchange.

She dresses for your plan rather than for the lobby: something that would pass at dinner downstairs, a coat over it, nothing a night manager would look at twice. In the lift she is one more guest going up, and if the evening begins with a drink below, she will already have found a table by the time you come down.

A hotel is not a condition of the call. A family house on one of the garden squares, a serviced apartment on Park Street, a friend's flat lent for the week: each is visited in the same unremarkable way. Inside Zones 1 and 2 the tariff is the whole of the cost, her car included. Further out, the only addition is a taxi there and back, and Cressida sets it beside the fee as one sum before you say yes.

One hour is the shortest length the Society arranges. It holds a drink, an honest conversation and an unhurried goodbye, and nothing is ever priced on top of it; there is no half hour either.

Many guests find that an hour closes too soon and begin instead with ninety minutes at £900, or with two hours at £1,100 when a supper is coming up from the kitchen. If an evening is going well, mention it to your companion before the time is up. Should her diary allow, Cressida confirms the extra time in writing and nothing else changes.

Two of the circle live in Mayfair itself. Angelika is free from seven on most evenings and seldom strays far from the square. Luna takes calls from Monday to Thursday and tends to arrive with an opinion on whatever the minibar holds. Michelle replies quickly on almost any night and can settle a nervous guest before her coat is off. After nine, Jasmin is glad of plans made the same night, and Tina says yes at short notice more often than anyone. Michelle, Jasmin and Tina are among the brunettes of the roster.

For guests still deciding where to stay, the After Dark Notes cover hotels with a private entrance habit and weigh up the new grand hotels of Grosvenor Square.