As with all stories by the great Conan Doyle there's always an underlying meaning, not that you'd wish to give this tale more weight than it carries, it is after all first and last a  story of a secret. Somewhere however runs the thread of honor and dishonor.

Lawyer John Albamore arrives at the Torins mansion a little after nine. Michael about to turn twenty-one is quiet and  afraid. Mr Cartwright at first talkative, affable becomes paler as the hour goes later towards midnight. It's as if all his life he has been waiting for this moment. It is seven years since the death of his father and five years since his mother died and at the hour of midnight when he comes of age he will open the black door to discover the secret of his inheritance.