Oscar winner Helen Mirren stars in an epic and romantic Sky original about the power, politics and passions of legendary Russian empress Catherine the Great.

General Rumiantsev leads the Russian army to a resounding victory against the Ottoman Empire, acquiring vast swathes of territory. Catherine summons Potemkin, who played a starring role, back to St Petersburg, which he takes as a sign they are about to begin their romance in earnest after the untimely interruption of war. But there is a nasty surprise waiting at Court: Catherine is in a relationship with a young guards officer, Alexander Vasilchikov, who the ever-canny Panin has manoeuvred into position during Potemkin's absence. When Catherine shows no sign of ditching dull Vasilchikov, Potemkin becomes increasingly frustrated and provocative.

Catherine struggles to deal with Potemkin's moods and jealousy. Then, tragedy strikes for Paul, forcing her to resort to extreme measures.

Catherine and Potemkin return to St Petersburg after the glorious Dnieper tour. It is not long before the Ottomans declare war, provoked by Russia's display of imperial aggrandisement in former Turkish lands. Potemkin - older and growing more ill by the day - is forced back out to fight for Catherine and for Russia. Catherine makes Potemkin supreme commander of all the armed forces and he begins his siege of the supposedly impregnable fortress of Ochakov. Potemkin delays the invasion for several months and the Empress begins to worry that the aging commander has lost his nerve.