Starring Mohanlal in the lead role, 'Thanmathra' tells the story of a man who leads a joyful life with his devoted wife and two children. However, he begins to experience memory lapses and becomes disoriented. Eventually, he is diagnosed with Alzheimer's disease, which deeply devastates his family.

A share broker becomes uneasy when a stranger, claiming to be his friend, moves into his house. He soon learns that the stranger is seeking revenge after being wrongly accused of a murder.

Madhavan, a villager, encounters Pavan, a young boy who lost his family in the Gujarat earthquake. He warmly welcomes Pavan into his family, and their bond grows stronger over time.