Valentina Villalba Rangel (Lucero) is a successful businesswoman and the heiress of a great fortune that her parents left to her upon their untimely death during Valentina’s childhood. Valentina has been raised by her aunt, Isabel Rangel (Silvia Pinal). She lives in a beautiful mansion in Mexico City with her aunt; her cousin, Ivana Dorantes Rangel (Gabriela Spanic); and her faithful nanny since her birth, Benita Garrido (Ana Martín). Valentina is a generous woman who shares her fortune and home with her aunt and cousin. But Ivana (Isabel’s only child) is consumed with envy and jealousy toward Valentina and believes she deserves everything her cousin has.
Valentina is in love with and engaged to marry Alonso Peñalvert (David Zepeda). Unbeknownst to Valentina, Ivana and Alonso are having a secret affair and are conspiring to rob Valentina of all she possesses. At the same time, Alonso is unaware that Ivana has an additional lover, Oscar Ampudia (Claudio Baez), who is married. Just prior to Valentina’s wedding day, Ivana runs over Oscar with his car and kills him.
Alonso stands Valentina up at the altar of the church on their wedding day but does not escape with Ivana as they had planned. Instead he flees Mexico and the loan sharks to whom he is deeply indebted. Devastated over Alonso’s betrayal, and unaware of Ivana and Alonso’s secret relationship and also of Ivana’s affair with Oscar Ampudia, Valentina changes from a young sweet, fair, and sensible woman into a cold, authoritarian, and despotic woman, full of bitterness. She swears never to fall in love again and decides to isolate herself at her family’s hacienda, “Los Cascabeles”, where she intends to live while managing the hacienda. At “Los Cascabeles” and the neighboring community she becomes known to all as “La Vibora", Spanish for viper or snake, due to her implacable and cold-hearted personality.
There she meets her neighbor, José Miguel Montesinos (Fernando Colunga), an attractive, intelligent, sensitive man who falls immediately in love with her beauty and strong personality. With his father and mother, Federico (Eric del Castillo) and Leonor Montesinos (Jacqueline Andere), José Miguel has relocated from Mexico City to his family’s rundown and neglected hacienda due to his father’s poor health. Despite the poor financial state in which his family finds itself, and against his mother’s wishes, José Miguel is determined to make the hacienda profitable as it was during his youth and a haven for his sick father.
Valentina’s aunt, cousin, and nanny decide to join Valentina at “Los Cascabeles”. Thus begins a story of lies, deceptions, duplicity, and treachery in which José Miguel must fight for Valentina and for her love against not only Ivana (who has fallen in love with José Miguel) but also against the wishes of his own mother and Valentina’s ranch foreman, Rosendo Gavilán (Sergio Goyri) (who has fallen in love with Valentina). Additionally, José Miguel must fight Alonso Peñalvert who has returned and comes to “Los Cascabeles” to convince Valentina of his love and to win her back.