Berlin 1948 is set in the city of Berlin during the Cold War. The city is split into West and East Berlin, and the USSR has all supply routes into the city cut off. In order to prevent West Berlin from being overrun by the Red Army, the US Army has smuggled an atomic bomb into the city. The bomb disappears, and it is up to you to find it before it falls into Stalin's hands.
You play a US spy in the CIA, Sam Porter, and have to travel all over the city looking for the bomb. You can walk around, or you can go to various destinations by taxi. You talk to many characters along the way, and interact with a number of objects in order to unravel the mystery. Most of the Berliners have nothing to offer you, so you are challenged with finding the ones who do. Some will tell the truth, some will lie, and some don't even know they possess information that would be of value.
Source: Wikipedia, "Berlin 1948", available under the CC-BY-SA License.