Fringe Season 3 Episode 6 - 6955 kHz

In the prime universe, Walter is dismayed to learn that Peter is continuing to study the blueprints from the doomsday device. Meanwhile, fifteen people suffer retrograde amnesia after listening tonumber stations. The team discovers that there is a hidden signal buried in the radio transmission, leading them to a strange cube-like device which is assumed to be the cause; the device is revealed to be from the parallel universe, and the shapeshifter controlling them is using them to wipe the memories should the listeners solve the numbers in the station. Walter and Astrid solve the numbers; they are a series of coordinates throughout the world. When they arrive at a location in New Jersey, the team discover the coordinates lead to parts of the doomsday device. In the parallel universe, Olivia attempts to arrange another test, but a hallucination of Peter tells her she has to return home.

Air date: November 11, 2010

Reference: http://en.wikipedia.org/wiki/Fringe_season_3