Mystery in game (6)

I believe the answer is:

enigma

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'mystery in game' is the definition.
'enigma' can be an answer for 'mystery' (synonyms). I am not sure about the 'in game' bit.

'mystery in game' is the wordplay.
'mystery' indicates an anagram.
'in'+'game'='ingame'
'ingame' is an anagram of 'ENIGMA'.

Can you help me to learn more?

(Other definitions for enigma that I've seen before include "German military cipher machine" , "Mysteriously puzzling person or thing" , "Mysterious puzzle" , "'Puzzle, riddle (6)'" , "Solution to mystery" .)

I've seen this clue in The Irish Independent.

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