The Shadow on the Glass: A Mr. Quin Short Story

At Mr. and Mrs. Unkerton's party at Greenways House, Mr. Satterthwaite learns that the house has a haunted window; no matter how many times it is replaced, the image of a gentleman in a plumed hat always seems to come back. He looks very much like a Cavalier soldier, a supporter of the King, from the English Civil War of the 1640s.

Then gunshots are heard, and Satterthwaite finds that two of the guests have been shot dead - soon followed by a sighting of the gentleman in the once-again newly replaced windowpane. Can Mr. Quin shed light on the mystery?