Sophia Frederica (Dietrich) is the daughter of a minor German prince and an ambitious mother. She is brought to Russia by Count Alexei (Lodge) at the behest of Empress Elizabeth (Dresser) to marry her nephew, Grand Duke Peter (played as a half-wit by Jaffe in his film debut). The overbearing Elizabeth renames her Catherine and reinforces the demand the new bride issue an heir to the throne.

Unhappy in her marriage, Catherine finds solace with the womanizing Alexei, first and foremost a paramour of the much-older Elizabeth. Rebuffed at this discovery, she takes lovers among the Russian Army to court its favor. When the old Empress dies seventeen years into their marriage, Peter ascends to the Russian throne and takes steps against his wife. Soon Catherine plots and exercises a coup, beginning a reign as Empress that will leave her known to history as Catherine the Great.