Series premiere. Following a palace coup that overthrew her unpopular husband, the Empress of Russia Catherine the Great faces challenges on all sides, including from her unfaithful lover Grigory Orlov, who's trying to force her into an ill-advised marriage; her resentful son Prince Paul who looks for greater political power as he comes of age; and enemies who call for the restoration of former infant emperor Ivan VI, imprisoned for nearly two decades. Seeking to freshen things up, Catherine invites the charismatic Lieutenant Grigory Potemkin to Court and the two instantly connect, with Catherine drawn to Potemkin's candor, integrity and vision. Later, Catherine must make a difficult decision regarding a disillusioned soldier who looks to oust her as war with the Turks looms.

Two years later, Potemkin returns to St. Petersburg, following the Russian army's resounding victory against the Ottoman Empire, but is frustrated to learn Catherine has taken up with a young officer, Alexander Vasilchikov. As Catherine and Potemkin flit around their feelings for another, Catherine's trusted confidante Countess Bruce puts aside her own desires to convince the Empress to give love a chance, leading to the beginning of what will become Catherine's greatest partnership. As a Cossack named Pugachev stirs discontent in the countryside, Catherine looks to Potemkin for advice and decisive action. Meanwhile, a newly-married Paul sees a future commanding the military, worrying his mother, who seeks to keep him in his place.

Eighteen months into their romantic relationship, Catherine and Potemkin experience difficulties as Potemkin longs for adventure and Catherine is drawn to her handsome secretary, Peter Zavadovsky. Potemkin's attempts to convince Catherine to expand southwards and take Crimea put him in direct opposition to Panin, whose cautious foreign policy favors an alliance with Germany. In the wake of an unexpected tragedy, Catherine reveals the brutal truth about Natalia to Paul and takes a special interest in her new grandson, causing Paul to turn decisively against his mother. After coming to an arrangement to preserve their deep political and spiritual connection, Catherine and Potemkin look ahead towards their shared dream of Russia's future.

Series finale. Following a declaration of war by the Ottomans, Catherine makes a weary Potemkin supreme commander of the armed forces and he's forced to fight once more for Catherine and Russia. An embittered Alexei and Paul plot to bring down the Empress by exploiting her new lover, the vain and power-hungry Platon Zubov. Catherine and Potemkin's failure to see eye to eye on how to respond to a joint ultimatum by Britain and Germany threatens the heart of their relationship. As her reign draws to an end, Catherine becomes increasingly paranoid and despotic, handing greater power to Zubov and setting out to change the line of succession.