Tells the story of the discovery of a vast and ancient lake under four kilometres of ice in the middle of the Antarctic ice sheet, near the Russian base of Vostok. Its existence was first mooted in the 1970s by a British team using airborne radar to map the area, but was not confirmed until some 20 years later by remote sensing satellites. Biologists believe that, because the lake has been cut off from the rest of the planet for 15 million years or more, microbial life in it could have been evolving independently into unique forms in conditions similar to those found on Europa, the icy moon of Jupiter. A recent discovery in Romania supports the idea of life surviving in Lake Vostok. 33 unknown species were found in a limestone cave near the Black Sea resort of Moville, which had adapted to live on chemicals found in the cave's pools. Instead of using light to photosynthesise, the microbes used hydrogen sulphide in the water as their energy source - a process known as chemosynthesis. The problem facing scientists at Vostok is how to explore the lake without contaminating it. Contributors to the programme include: Profs John Priscu, Montana State University, Andrei Kapitsa, Moscow State University and Ken Nealson, NASA Astrobiology Group, and Drs Frank Carsey, NASA Jet Propulsion Laboratory, Robin Bell, Columbia University, Cynan Ellis-Evans, British Antarctic Survey, Jean Robert Petit, Vostok Ice Core Project and cave biologist Dr Serban Sarbu.