Eisenstein died before Ivan the Terrible III could be completed. We're lucky enough to have two. Stalin disapproved of it, and we're very lucky he didn't have it destroyed. Around 20 minutes of III was completed, but most of that was lost. All that is left is one scene where a German Knight offers his services as a soldier trainer to Ivan and his court. Like the first two Ivan films, the images are frightening. Maybe even moreso, here, since Ivan and those surrounding him have grown even more sinister and insane. Fyodor Basmanov creeps around the room as if he is stalking prey. They taunt the German knight for lying to them and show him what they did to the last foreigner who lied to them by opening a very Jaba the Hutt-like pit. They stare into it in horror, then Ivan claims to have been joking in his threats, and offers the knight a place in his Oprichniki (Secret Police).
Also, a screen test exists for the actor (yes, actor) who would play Elizabeth I. Supposedly the government disapproved of it, possibly because it was homoerotic.
As for the rest of the film, a screenplay may exist, but here are the parts of the plot I know were going to be included: Fyodor Basmanov was going to be prompted by Ivan to kill his father, Alexei, and then Ivan was going to use that as evidence that he would betray anyone, thus having him killed. Ivan was later going to have a confession before a giant fresco of the Last Judgement (of which a photo exists; I think they actually filmed at least part of this scene, for there are stills) while a priest read a list of people whom he executed, over 1500 in all. After this, Ivan leads a battle against Livonian troops whose general is Kurbsky, whom we last saw at the opening of part II. Ivan wins, and thus wins access to the sea for his people (which, you may remember, the young Ivan in the prologue swore that he would win back for Russia). The final sequence of the film would apparently been Ivan walking towards the waves on the beach, then there would have been a shot so that we could see behind him Russia and her people in horrible ruins.
All of this information can be found on the Criterion DVD set, Eisenstein, The Sound Years, possibly the best DVD that Criterion has released yet.
