I am a movie director and I just received the following movie plot. Could you help me answer this question? If not, let me know by writing "Not answerable". Plot title: Terror by Night Movie plot: An off-screen narrator tells of the deadly curse carried by the fabulous "Star of Rhodesia" diamond, then takes us to a London coffin-maker's, where Vivian Vedder (Renee Godfrey) arranges a special coffin for her late mother. She'll be taking it on the 7 PM train to Edinburgh. At Euston Station, Roland Carstairs (Geoffrey Steele) meets Holmes (Basil Rathbone), whom he has hired to guard his mother Lady Margaret (Mary Forbes), who has already boarded the train back home to Scotland. Actually, he's there to guard the Star of Rhodesia, which she has owned for many years, but was the object of an attempted theft when Lady Margaret wore it at a royal function. Holmes is certain the thieves will try again. Apparently, Scotland Yard agrees, as Inspector Lestrade (Dennis Hoey) is also taking the trip. The train begins to pull out, and Watson (Nigel Bruce) and his old army friend Major Duncan-Bleek (Alan Mowbray) barely manage to board. They had bumped into each other, and forgotten the time as they reminisced. Carstairs brings Holmes to his compartment, where his mother is skeptical about the aid of a "policeman", but she lets Holmes examine the Star.While Holmes, Watson, Duncan-Bleek, and Lady Margaret are in the dining car, Carstairs falls onto the floor of his compartment. Lestrade hears the thud, but finds the door to the Carstairs compartment locked. Holmes arrives and has the attendant (Billy Bevan) open it. They find Carstairs dead and the box that had contained the Star empty. The body shows no wounds aside from a tiny spot of blood, but Holmes declares it's murder, since a thief arriving right after Carstairs died of natural causes is too improbable. Watson, unimpressed with Lestrade's plodding, decides to try questioning suspects himself. (Thus suspects are those who occupy compartments in the same car, as the attendant was at the door to the leading car, and the trailing car is the locked luggage van.) Watson gets nowhere at all in his attempt with cranky William Kilbane (Frederick Worlock), a professor of... My question: What gets stolen?
The answer to this question is:
Diamond