Cathryn Harrison (Jane Hardy) was the granddaughter of Rex Harrison and the daughter of Noel Harrison.
When the police are quizzing about the box which has just arrived on an aircraft, several times the characters mention The Scilly Isles. Cornwall people would not call them this. They would use the correct title. The Isles of Scilly.
John Bleasdale (Warder) and Cathryn Harrison (Jane Hardy) were both in the Poirot episode 'Death in the Clouds'.