Mason Powers, a former CIA agent, awakens in a Turkish asylum with many of his memories erased. Gradually recovering from his amnesia, Mason realizes that he has been locked up for allegedly murdering his supervisor. Convinced that he is innocent, Mason eventually escapes from the mental hospital. However, that brings him back to his old job, where he becomes entangled in a world-wide conspiracy of espionage, terrorism, and murder.

Countdown is an adventure game with emphasis on traveling and conversation, though inventory-based puzzles are present as well. Over the course of the game the protagonist travels to many different locations around the world, though the areas themselves are fairly small. Interaction is performed by choosing verb commands such as Look, Get, Taste, and others. There are no "hot spots" that indicate than an object can be interacted with. A bulk of the game is dedicated to conversations, which include, among others, special commands such as Help, Hassle, Pleasant, and Bluff. Sometimes choosing a wrong action may lead to a premature end of the game.

A few segments involve navigating top-down mazes. It is possible to die in various ways and also get irrevocably stuck. The game imposes a time limit of ninety-six in-game hours on the player. Certain actions - such as spending more money and traveling by plane instead of a train - may help the player stay well within this limit. The game is notable for using digitized photography alongside hand-painted graphics, character portraits are all scanned photos. It also uses digitized music and speech samples, which can be heard even with a PC speaker thanks to a special software.