Secret Mission plays in Opalia, a small kingdom in south-east Asia in the 1950s. Because of its geographical position the two superpowers, the USSR and the USA, are highly interested in the country. Their agents have destabilized the country, and local rebels, led by Prime Minister Vishaka, plan to assassinate the king. You play Jeff, a double agent, and when you arrive in Opalia, you are ambushed. You wake up in your hotel without remembering who you are and what you are doing here. Soon you learn who you are and what your mission is: to find evidence for the Minister's devious scheme. A complicated mission, as both countries are after his plan and both have their own motives.

Secret Mission is an inventory-based adventure with a big variety of puzzles, including the for the genre familiar ones (decoding messages, cracking safes). The game is completely controlled by the keyboard and features voices and subtitles.