Sir John Appleby dines one evening at Allington Park, the Georgian home of his acquaintance Owain Allington, who is new to the area. His curiosity is aroused when Allington mentions his nephew and heir to the estate, Martin Allington, whose name Appleby recognises. The evening comes to an end but just as Appleby is leaving, they find a dead man - electrocuted in the son et lumihre box which had been installed in the grounds.