Jack Hardy (Jason David, A Touch of Frost) is the sole survivor of a mysterious submarine disaster in World War II. Now, in 1981, the ill-fated submarine has resurfaced, miraculously intact, but what’s waiting for the new crew under the grey waters of the Baltic Sea turns out to be much worse than the Russian submarines they were expecting. Hardy fights for his life as the forgotten events of 1943 start to have deadly consequences for the modern day crew of the submarine. Wherever this submarine has been all this time, it’s brought some bad luck back with it.