Kings Cross escorts in N1C and WC1X, from the concourse to Coal Drops Yard

The change here happened within a decade, and the joins are still visible in the best way. Coal Drops Yard holds two levels of small shops and dining rooms along the old viaducts, with the roofs rising to almost touch above the middle. Granary Square sits behind it in front of the art school, with the canal below and wide steps down to the towpath where people sit until the light goes. Gasholder Park is a minute west, a cast iron frame with a lawn inside it and a mirrored canopy overhead.

South of Euston Road the register changes completely. Argyle Square and Percy Circus are Georgian and residential, Kings Cross Road runs down towards Clerkenwell past small terraces, and by eleven the noise belongs entirely to the station. Kings Place stands apart from all of it on York Way, a glass block on the canal with two concert halls underground, the one room in the postcode that keeps a curtain time.

Arrivals, mostly. Guests off the late services from Leeds, York, Newcastle and Edinburgh, who reach the concourse at ten and have no wish to spend the evening alone in a room three minutes away. Visitors staying near the station for a conference at the art school or a concert on York Way. And a steady number of people living above Granary Square, who like an evening they can walk home from.

Bookings skew late and often short: an hour at £250, or £400 for ninety minutes after a long journey, with the ten hour night at £1,800 the usual choice when the return train leaves before nine the next morning.

The Great Northern Hotel curves along Pancras Road exactly as it did when it opened beside the first trains, a long sweep of brick with a narrow ground floor bar and corridors that follow the bend of the building. The Standard London faces it across Euston Road, a red brick council block from the seventies reworked behind an external glass lift, with a bar on the tenth floor looking straight at the Gothic front opposite. The Megaro sits on Belgrove Street a minute from the taxi rank. The Gyle is the small house on Argyle Square, a few streets south into WC1X.

They appear as buildings a companion walks into, not as associates; no agreement links them to us and none is sought. The apartments above Granary Square and the flats around Percy Circus are visited on the same footing.

King's Cross St Pancras, one minute from most N1C addresses and the largest interchange on the network: Circle, Hammersmith and City, Metropolitan, Northern, Piccadilly and Victoria, with the mainline platforms above them. Euston, ten minutes west along Euston Road on foot.

For guests flying in, the Piccadilly line arrives from Heathrow at that same station without a change, which is slow but asks nothing of a tired traveller. Both postcodes sit in Zone 1, so the journey is already counted inside the fee.

A message sent from a moving train is perfectly normal here. Give the hour you expect to be in the room rather than the hour the train is due, add how long you would like, the address, plus a name you have chosen or a couple of lines sketching the company you want. The reply takes 10 to 15 minutes at any point in the night, and text you can copy is on the booking page.

A single message settles who the room is under, which building, and which door. That single message puts an ordinary booking on the sheet. Anything running to breakfast, any event, and any trip beyond London is fixed the same way, with the train times written in beside it.

From confirmation, an N1C door is usually reached inside the hour, and a late train simply moves the hour rather than losing it. Three clear hours cancels at no cost, under two hours leaves half the fee standing, an unanswered door is charged in full, and a quarter of an hour either way is treated as grace.

20:00, a first drink on the tenth floor across Euston Road with the lit front of the station filling the window, the best free view in either postcode. 21:00, down and across to Coal Drops Yard for a table under the viaduct, where the kitchens run late because the trains do. 22:30, ten minutes along the towpath to the canal steps at Granary Square, empty and lit at that hour. 23:15, back up to the room with the concourse still announcing departures behind you.

Three hours at £700 covers that comfortably. Drop the walk and two hours comes to £500; after a long journey, ninety minutes at £400 buys a drink and an hour upstairs. Ten hours at £1,800 runs through to breakfast and is the sensible answer to an early departure.

Nobody on the list keeps a home address in either postcode, so arrivals are measured from the south and the west. Tina comes straight up Grays Inn Road from WC2 in about fifteen minutes and takes short notice better than anyone. Nora travels across from Paddington on one line without a change, athletic, honey blonde and easy to be around at the end of a long day. Roxi has a direct run in from Pimlico on the Victoria line, which late in the evening beats most cabs.

Everyone else in the company reaches Kings Cross on the same figures, with the travelling already inside the fee.

Next door under the Gothic front, St Pancras handles the continental arrivals. Ten minutes west along Euston Road is Euston and the trains to the north west. South down Grays Inn Road, Bloomsbury begins at the first garden square, with Holborn and the Inns a few minutes beyond it, and Covent Garden about fifteen minutes further on.