As the game begins, the player's character is spending a final day of a London vacation in the Kensington Gardens.

Time begins to slow as the missile approaches, and with some ingenuity the player's character finds an incongruous door hovering in mid-air.

Exploring this new environment, the player finds several other mysterious doors, each of which leads to another chapter in the history of nuclear weaponry.

After visiting test sites (including ones in Siberia, Nevada, and the Eniwetok Atoll) and Nagasaki just before each device is detonated, the player has one scenario left to deal with.

The final door leads to the New Mexico desert on July 16, 1945, mere minutes before the test-firing that will change the course of history.

The Eniwetok Atoll test took place in the middle of the ocean; hence it is symbolized by Neptune, the Roman god of the sea.

The fictional incident in London was chronologically the latest to take place, and omega is the last letter of the Greek alphabet.

The fictional Low Earth Orbit (Mercury) detonation is very likely a reference to the space interceptor subproject of the Strategic Defense Initiative, nicknamed "Star Wars", contemporary with the game's development.

... this is not only one of the most socially and politically powerful game experiences ever created, but also a landscape upon which puzzles of trademark Infocom quality can appear.