What is the meaning of the italicized sentence in this paragraph?
From basement to sky rise the tenements of an alien colony. Their windows slot the ebony of their walls with lemon. Behind those windows, strange life is moving, dressed with forms that are not of London or of England, yet, in essence, the same agreeable life that you have been living, and tonight will live no more.
It's a part of the novel "The hands of Mr. Ottermole" by Thomas Burke.