This deeply moving film follows the paths of guilt and bereavement in three intertwined families. When Masoud Kia drove his wife, son and daughter into a head-on collision, all three of them died. Masoud himself would have passed away had he not received a timely kidney transplant from a stranger named Reza. Grief-stricken and suicidal, he accosts Reza's wife, Leila, and their daughter, Setareh, accusing them all of saving him against his own wishes. But Reza himself has passed away, and Leila spends lonely nights with family photos, even as she hides the truth from her young daughter. Meanwhile, she comforts the young neighboring couple as they argue over whether to get an abortion or to bear a child into poverty. The doctoral student husband, Peyman, insists that they can build a family only after they complete their studies, but his wife Sara hopes to save their child. Skillfully woven together by memories and flashbacks, Lost Truth presents a story of grief that is both poignant and beautiful.