The year is 1779. Karim Khan, founder of the Zand Dynasty, ruler of Iran, the self-styled Advocate of the People, has died. He is succeeded, as in OTL, by his son, Mohammed Ali Khan. However, Mohammed Ali Khan, who died after a few months in OTL, does not die in this timeline. When his weak and lazy brother Abu al-Fath dies of a heart attack just like in real life, Mohammed Ali Khan remains the sole ruler of Iran.
Under Mohammed Ali, Zaki Khan never gains as much influence as he did in OTL, because Mohammed Ali is a much more competent monarch than Abu Al-Fath. Mohammed Ali's soldiers manage to kill Agha Mohammed Khan before he can escape and rally the Qajars, thus preventing the Qajars from posing a meaningful threat to the Zand Empire. Mohammed Ali continues his father's policies, and firmly establishes Zand control of Iran.
In 1784, the Zand Empire was doing fairly well. Instead of political instability and war both external and internal, they had four years of prosperous peace under Mohammed Ali Khan. The Advocate of the People of Iran would lead the Zand Dynasty forces in a war against the collapsed remains of the Afsharids this year, and would defeat the last of the Afsharid Shahs by 1787. This victory unified Iran under one ruler for the first time since the death of Nader Shah in 1747.