All he knew was that this mysterious benefactor had walked away in an opposite direction to that in which the cab had gone, and had vanished into the night.
Tarling frowned.
"That's curious," he said.

"Get me another taxi." "I'm afraid you'll find that difficult, sir." The hotel porter shook his head.

"You see how the fog is--we always get them thick about here--it's rather late in the year for fogs..." Tarling cut short his lecture on meteorology, buttoned up his coat, and turned out of the hotel in the direction of the nearest underground station.
The hotel to which he had taken the girl was situated in a quiet residential street, and at this hour of the night the street was deserted, and the fog added something to its normal loneliness.
Tarling was not particularly well acquainted with London, but he had a rough idea of direction.

The fog was thick, but he could see the blurred nimbus of a street lamp, and was midway between two of these when he heard a soft step behind him.
It was the faintest shuffle of sound, and he turned quickly.
Instinctively he threw up his hands and stepped aside.
Something whizzed past his head and struck the pavement with a thud.
"Sandbag," he noted mentally, and leapt at his assailant.
As quickly his unknown attacker jumped back.

There was a deafening report.