The ship, carrying a consignment of arms for the Algerian revolutionary movement, leaves for Tangier. Bulgarian counterintelligence intercepts a letter leaking the precise dates of the ship's departure and arrival. Only four people know about the actual mission of the ship: among them - Izmirski and Ben Salal. The investigation begins. Meanwhile, the ship is intercepted by foreign warship in the open sea. Ben Salal is assassinated abroad. Izmirski escapes and makes his way back to Bulgaria. State security officer Donev works hard to identify the traitor. This is Izmirski. He has got rid from Ben Salal as an unwanted witness to the big bribe he has taken. The whole business about the ship has been merely a cover-up for the mission of another ship with the arms, which reaches its destination undisturbed.