Ayatollah Ruhollah Khomeini returns to Iran after 15 years in exile. Very quickly after arriving, Khomeini begins efforts to reconstruct Iran according to his own religious vision. During his years in exile he had developed an ideal called "Rule of the Jurist" in which the clergy were called to govern.
Ayatollah Khomeini experiments briefly with a parliament, but ends that quickly when he realizes that he cannot control them well enough. Khomeini will next bring together an "Assembly of Experts" to draft an Islamic constitution. They, of course, create a state which will be led by Khomeini (who is named Imam and declared leader of Iran for life) and run by the clergy.
Some Shi'ite religious leaders will raise objections because they still believe that government should be independent of clerics, but they will be ignored. Over time, Khomeini seems to reconsider these objections because disagreements among the clergy over political matters will at times threaten the stability of the Iranian government.
There will even be occasions when Ayatollah Khomeini calls upon the clergy to return to their "proper profession" rather than be involved with government.