After completing his education, a young man named Pertev came to Istanbul and settled in a hotel in Moda. One day, while walking with his fiancée Necmiye Hanım in Moda, an influential figure named Şekip Paşa saw Necmiye Hanım and took a liking to her. He had Pertev Bey arrested on charges of carrying dangerous documents. He managed to bring Necmiye Hanım to his own home with a letter written in Pertev Bey's name. Necmiye Hanım's neighbor was a gangster named Küçük Cemal. Upon learning of Pertev Bey's arrest, Cemal senses an attempt to attack Necmiye Hanım's honor. Through his friend Eftalya, he learns that Necmiye Hanım has entered Şekip Paşa's house. Together with a few friends, he raids the house and manages to rescue Pertev Bey, who is being held captive by Necmiye Hanım and Şekip Paşa, and escape with him.

Directed by Sadi Fikret Karagözoglu.

Considered as the one of the first feature-length Turkish movies produced during the reign of the Ottoman Empire, Casus is about a spying adventure which took place in the First World War. The copy of the movie did not survive to the present day.