Ang Magmamani tells of a mother and her daughter falling in love with the same man. Luis, a rich and handsome man from Manila, falls in love with Ninay, a peanut vendor he meets while he is travelling. His mistress, Tentay, accidentally sees Ninay’s picture in Luis’ possession and realizes that Ninay is her own daughter whom she abandoned years ago.
Tentay then decides to leave Luis and enters a convent. Meanwhile, Luis, desirous of having a well-educated wife, asks Ninay to study in a convent school. She coincidentally enters the school run by the convent that her mother retreated to.
Tentay and Ninay become friends inside the convent. However Tentay falls seriously ill and Ninay visits her on her deathbed. When the priest arrives to administer last rites, Tentay makes a shocking revelation – the priest is Ninay’s father, resulting in an unexpected family reunion.