Morteza, fifty years old, has just got out of prison when he is suspected of murdering a child who is found drowned by the edge of a lake.

Taher, the police officer in charge of the case, at first thinks Morteza is guilty, like all the evidence indicates, before discovering that he knows him. Their relationship goes back thirty years, and is rooted beneath the lake's deep waters.

Convinced of Morteza's innocence, Taher decides to prove it despite all appearances.