A particularly useful post for this episode can be found on the r/hisdarkmaterials subreddit. It provides a detailed breakdown of the episode's lore and key plot points:
: The discussion explains that the city's ruin and the Spectres' presence are due to the Guild of the Tower opening too many windows between worlds for trade and theft, which eventually tore the fabric of reality. His Dark Materials 2x4
S02E04 - Tower Of The Angels [UK Release] : r/hisdarkmaterials A particularly useful post for this episode can