Achuvinte Amma movie tells the deep rooted relation between a mother Vanaja (Urvashi) and a daughter Achu (Meera Jasmine). Vanaja (who is a street smart LIC agent who has made it on her own. She is smart in many things. She lives with her only daughter Aswathy alias Achu who holds a diploma in Civil Engineering. Mother and daughter share a special relationship and are like friends. There is nothing that Achu hides from her mother. But the only thing taboo in their life is the talk about her father. Vanaja never speaks about Achu's father and Achu never asks her as she doesn't want to hurt her beloved mother.
Their life moves smoothly until Immanuel John alias Ijo (Sunil Kumar) enters their life. They meet Ijo accidentally when they go to another town for attending an interview. After the first meeting, Achu and Ijo run into each other now and then, and a friendship develops between them.
Achu gets a job in a construction company. Ijo conveys his wish to marry Achu to Vanaja. Vanaja wants to meet his parents and then he reveals that he is an orphan. His family had committed mass suicide due to financial problems and he was the only one who survived. Now Vanaja turns against the marriage saying that she wants her daughter to get married to a solid family where there are lots of people to care for each other.
This shocks Achu and she raises the taboo and questions Vanaja about her father. Mother and daughter has a hustle- Vanaja does not reveal anything and Achu walks out of her home. She goes to Ijo but he asks her to go back home. Achu is adamant and she stays with her colleague. Ijo tries to mend the relationship between them but Achu takes no heed.
Meanwhile Achu due to uncomfortable circumstances, had to leave her colleagues place and she finds that she has no place to stay. She is totally worked up and meets with an accident and then Vanaja rushes to see her in hospital. Achu still doesn't speak to her and Vanaja opens her mind to Ijo and that's the crux of the story.