The investigation of the murder of two policemen will pit Inspector Vivancos, a tough, hardened and incorruptible guy, against his superior, Lieutenant Pajarda.

Located in Madrid's Plaza del Sol, Km. 0 is the point from which all distances in Spain are measured from the capital. In Km. 0, it is also the meeting point for a gallery of characters. Bored, affluent housewife Marga meets up with gigolo Miguel, who co-habitates with gay Benjamin. Sergio, a soon-to-be-married office clerk who can't wait to lose his virginity, makes the acquaintance of prostitute Tatiana, while gay dancer Bruno meets Maximo. Meanwhile, wannabe director Pedro arranges to meet up with Silvia, an actress who wants to work in musicals directed by Gerardo, and bartender Mario is caught between Amor, who wants to marry him, and her little sister Roma, who is truly in love with him.

On his way to Santiago de Compostela, a pilgrim recounts his experiences through the letters he writes to his friend.