Waterloo escorts, SE1. Parliament across the water, the City one stop away.

County Hall, for most of the twentieth century the seat of London's government, now holds a hotel, an aquarium and a line of restaurants along the Queen's Walk. The London Eye turns slowly beside it, 135 metres at the top, and from Westminster Bridge the view takes in the Elizabeth Tower, the river and, at dusk, the lamps coming on along the Embankment. It is the most photographed half mile in the city, and in the evening it empties faster than you would expect.

Follow the river east and the promenade runs past the Southbank Centre to Gabriel's Wharf and the Oxo Tower, whose eighth-floor restaurant looks straight across at St Paul's. Sea Containers stands just before Blackfriars Bridge. Behind the waterfront, the streets around the station are commuter territory, busy until eight and calm after.

Waterloo Bridge, rebuilt during the Second World War with a workforce made up largely of women, still gives the best view in London at dusk: Parliament and the Eye to one side, St Paul's and the City to the other. Cross it on foot as the evening begins and the plan for the night usually sorts itself out.

London Marriott Hotel County Hall occupies the old council building itself, and its river-facing rooms look directly across at Parliament. Park Plaza Westminster Bridge is its much larger neighbour at the foot of the bridge, a modern block with bars on the ground floor and hundreds of rooms stacked above. Sea Containers London sits further east on the riverbank, its interiors modelled on the great transatlantic liners. The Hoxton, Southwark is ten minutes inland on Blackfriars Road, informal and popular with a creative crowd.

We list them as buildings she walks into, never as partners; none has any arrangement with us. The same goes for a private flat off Stamford Street or a serviced apartment behind the station. You name the address, the desk checks the booking name and room number once, and the details go no further.

A guest at County Hall writes at six: three hours at £700, starting at eight. She is in the lobby at five to. They walk the Queen's Walk as the Eye lights up, take a table at a riverside restaurant, and are back at the hotel before eleven with Parliament floodlit across the water. She leaves at the end of the third hour, exactly as agreed, and the river keeps the rest of the night to itself.