What is a synonym for mystery?

Here are some synonyms for mystery, depending on the context:

Formal:

* Enigma

* Conundrum

* Riddle

* Puzzle

* Secret

* Intrigue

Informal:

* Whodunit

* Secret

* Clue

* Case

* Unsolved mystery

* The unknown

* The unexplainable

Literary:

* Mysterium

* Arcane

* Inscrutable

* Abstruse

The best synonym will depend on the specific situation. For example, "enigma" might be a good synonym for a mysterious person, while "whodunit" might be a good synonym for a crime mystery.