In February 1945 the submarine U-864 is on its way to Japan. On bord there is the crew, 18 German aircraft constuctors and two Japanese experts, as well as new power plants and navigation systems of Messerschmidt and secret plans for the ME-262-fighter. The Asian allies shall get modern technologies to win the aerial warfare against the US.
But on the Monsoon-route in the North Sea , in a depth of 140 metres, near the Isle of VÃ¥lje the mission comes to an end. Already before the submarine had left Bergen in Norway the Royal Navy could catch and decode a radio messages.
Thus the Royal Navy can waylay the U-864 with its own submarine, the "Venturer", which is equipped with sonar. On 9th of February the captain of the "Venturer", Lieutenant Jimmy Launders, can locate the motor sounds of the U-864, which moves in reduced spees due to a damaged diesel engine. The German commander Rolf-Reimer Wolfram already has ordered the return to Bergen to save his crew and the machinery, which was already paid in gold by the Japanese.
But it is too late. There occurs the only fight of two submarines actually under water. Despite the manouevres of the U-864 short after noon the "Venturer" can fire four torpedoes, which hit the U-864. The submarine sinks with all its 73 passengers in front of the Norwegian coastand with it also important military secrets of the Nazis, which could have changed the further development of the war.

60 years later a team under the lead of Dag Amerund tries to salvage the wreck of the U-864, which is an ecological danger, as there are 80 tons of mercury in it. If they would be damaged it would mean a catastrophy for the ecological system. Now the wreck shall disappear under a coffin made of concrete.
A camera accompanies the team and at the same time the history of the U-864 is reconstructed.
The dramatic events are revealed by German and English documents, interviews with the last two survivors and the British marine historian Eric Grove from Hull University.