"Thaththa" follows the tragic story of Neal, a desperate man who breaks a promise to his wife and takes one final robbery job to secure a better financial future for his children. The narrative shifts back and forth between Neal's final hours, where he lovingly teaches his son Dalip math and promises him a red bicycle, and the present day, where an adult Dalip visits Neal's grave to invite him to his sister Thrisha's wedding. The fatal job ends in a botched confrontation with an armed homeowner, leading to Neal's untimely death. Ultimately, the film explores the enduring legacy of a parent's flawed but profound love, culminating in a posthumous letter where Neal hopes his son will eventually understand the devastating sacrifices he made for his family.