El Noveno Mandamiento is a Mexican soap opera produced by Lucero Suárez in the year 2001.
The story occurs in a small Veracruz town where brothers Rodrigo and Bruno Betancourt vie with each other for Ana's love, thus breaking the ninth commandment, not to covet thy neighbor's wife.
Isabel suffers from diabetes. While she does not have a meek personality, ever since the death of her parents, she is easily manipulated by her sister Clara. Clara lives tormented with the thought that she will never marry, since in that small town, the only bachelor is her sister's fiance, Leandro, who initiates an uncontrollable passion in her.
The wedding between Isabel and Leandro is postponed because he must make an important business trip. Clara attempts to persuade him to call off the wedding saying that Isabel only has a short time to live, but he refuses to listen. On the contrary, Leandro and Isabel agree to spend the last night together before he leaves for the trip. They decide to meet in the stable, but Clara finds out. Along with her faithful servant, Andres, Clara plans an accident so that Isabel never makes it to the date. Instead Clara goes to the dark stable, with Isabel's perfume and dressed like her. Leandro, who has drank some drinks, spends the night with Clara. Isabel feels betrayed when she sees them together.
Clara makes Isabel think that Leandro was with her because he felt pity for her, since she was a dying woman. Clara pretends that she is pregnant and Isabel falls into a severe crisis, due to her diabetes, and thinking that she will die, makes Leandro promise that he will marry Clara.
Leandro is extremely unhappy attached to a woman whom he loathes, but does not give up and finds proof that Clara tricked him into sleeping with her. After Isabel realizes his innocence, they make love for the first time.
Andrés tries to steal the proof which incriminates Clara. But while fighting, Leandro falls and hits his head, losing his memory. Taking advantage of the situation, Clara Makes Leandro believe that they have always been a happy couple, but that her sister has always tried to come between them. Clara also threatens to kill Isabel, so she flees to Mexico City, where she discovers that she is pregnant.
Leandro regains his memory and Clara can no longer keep the lie of her pregnancy. When Leandro is about to abandon her, she causes another accident and blames Leandro for it. She makes him feel guilty that she has "lost" their child.
Tied by guilt and thinking that Isabel is with another man, Leandro stays with Clara in a rocky and obsessive relationship. Leandro unburdens himself with alcohol, always debating to stay or to go; Clara living with his rejections, while always desperately trying to make him love her, or at least keep him by her side.
Clara then asks a dying cousin to leave her newborn baby under her and Leandro's care. The cousin dies after making Leandro swear that he will be like a father to the baby. However, the baby also dies and Clara replaces her with the daughter of Andres, her servant. The baby is named Fabiola.
Isabel gives birth to a baby girl and names her Ana, but Isabel dies.
Time flies and Ana goes to Clara's ranch without knowing who her parents are. There she meets Fabiola, who grows up to be the owner of the ranch "Las Lágrimas" (The Tears). Ana also meets the neighbors, Rodrigo and Bruno Betancourt, heirs of the best lands in that region.
Fabiola is engaged to Rodrigo, but then Ana appears. Both brothers want Ana. Twenty years before, it was two sisters and one love, but then the story repeats itself, now, with two brothers and one love.
Daniela Castro is Isabel and Ana
Armando Araiza is Leandro
Chantal Andere is Clara (young)
Salvador Sánchez is Andrés
Francisco Gattorno is Rodrigo
Ana Patricia Rojo is Fabiola
Alma Muriel is Clara (older)
Alex Ibarra is Bruno