Captain Giorgio Bachetti of the Italian military finds himself at a remote base in 1863. He is engaged in a passionate relationship of letters with his beautiful mistress from home, Clara. At the base, however, he catches the attention of the Colonel's sickly cousin, Fosca. She soon not only falls in love with Giorgio, but also becomes obsessed with him. Giorgio attempts to resist her attempts, but eventually he begins to appreciate her total devotion and ends up sleeping with her before she passes away.