slipping into darkness

Proszę o pomoc, co oznacza "slipping into darkness".

Całe zdanie:
(The whole quarter was slipping into darkness.)

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Garrett felt no sense of foreboding when he – just like every week - was on his way to the meeting place with Victoria’s emissary. The whole quarter was slipping into darkness; the streets were slowly emptying of passersby; snow was falling and covering the whole city with a fine coat of white powder. Garrett was stealing through the shadows, although there was nobody in the vicinity. He was thinking about the new task that his old enemy would certainly give him. When would this finally end?

wieczór był

Jak ładnie przetłumaczyć zdanie, o które zapytałem?

przykladowo:
... pogrążało się w ciemności.