Cambridge dictionary defines a circumstance as "a fact or event that makes a situation the way it is": literally, it means things that are standing around a particular situation. Halpin's question refers to what has just happened (the transfer to the fourth dimension). The protagonist's reply is probably intended to indicate that the transfer is irrelevant to what is about to happen (the protagonist murdering Halpin).
It's certainly a very unusual usage of the word: firstly because we normally talk about "circumstances of" rather than "circumstances to": and secondly because we generally use it only about things that happened in the past, or about hypothetical future situations- we don't tend to use it for planned future events.