Explanation:

• Emissary (Option 2): This word means someone sent on a special mission, usually as a diplomatic representative. It fits well for someone going on a secret official mission.

• Epicurean (Option 1): Refers to someone devoted to enjoying good food and comfort. It lacks any connection to secret missions.

• Celibate (Option 3): Describes someone abstaining from marriage and sexual relations. This is unrelated to the context of a secret mission.

• Rogue (Option 4): Generally means a dishonest or unprincipled person. It doesn’t align with the idea of a secret official mission.