: Lyra and Will must use the knife to retrieve the Alethiometer from Lord Boreal (Sirs Charles Latrom), who stole it from Lyra earlier in the season.
: 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
: This episode also features Lee Scoresby finding Stanislaus Grumman (John Parry), who is revealed to be Will's long-lost father. : Lyra and Will must use the knife
S02E04 - Tower Of The Angels [UK Release] : r/hisdarkmaterials S02E04 - Tower Of The Angels [UK Release]
Are you interested in a or more details on how the Subtle Knife works ?
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: