The film begins in the 1980s Soviet Union. Two best friends, Orlov and Muravyev, are serving at the Black Sea Navy Base in Sevastopol, Crimea. Both fall in love with one beautiful girl Nelly, and their friendship suffers a first blow. Because she picks Muravyev, his friend Orlov struggles with an inferiority complex and becomes a secretive alcoholic. After the collapse of the Soviet Union in 1991, both friends are transferred to the Northern Fleet on the Polar Ocean. One day their sub is performing a routine training. A disturbed WWII mine slowly moves on a collision course with the sub. A mighty blast knocks down everyone inside the wrecked sub, 72 meters below the sea level. Then ensues a nerve-racking struggle for survival.