Conversation so far:
Who was Helen Duncan?
the medium Helen Duncan.
How was Harry Price connected to Helen Duncan?
Price had proven through analysis of a sample of ectoplasm produced by Duncan, that it was made of cheesecloth.
Did he invesitgate other things related to Helen?
Duncan reacted violently at attempts to X-ray her, running from the laboratory and making a scene in the street.

Question: What other involvement did he have with Helen?
Self-contained rewrite: What other involvement did Harry Price have with Helen besides the laboratory incident?