A mystery is an unexplained event or situation. The word is a reference to a matter of mystification, where causes of situations are not understood. The common usage can also be highly sarcastic, referring to the obvious. In most cases the literal usage is based on extension of grammatical usage and works as a noun in referring to the subject.
Examples of Mystery:
Sarcastic: The mystery of the missing car keys in your pocket.|
Literal:The whereabouts of the missing financial adviser is a mystery.
Literary: The Agatha Christie Murder Mysteries.