It's my 50th shortly, and we are going to see Macbeth.  A number of people coming don't normally 'do Shakespeare', so here is a brief guide to help make sense of the play. In summary the plot is:

• Macbeth learns from the witches that he is to be King

• The king (unexpectedly to Macbeth) declares his son, Malcolm, as heir

• Macbeth kills the king to take the crown for himself

• Malcolm flees to England

• Macbeth becomes paranoid and kills people to protect his position and line of heirs

• Macbeth becomes overconfident because the witches say he can't be killed unless certain seemingly-impossible conditions are fulfilled

• At the end of the play, the King's son returns from exile, the witch's impossible conditions are fulfilled, Macbeth is killed and the King's son takes the throne

Beneath superficial and sub-plot differences, the plot of Macbeth is similar to the film Gladiator, though with one important difference. In Gladiator, the soldier (“Gladiator”, or Maximus) is the hero, and Caesar's son (Commodus) is the villain, but in Macbeth the soldier (“Macbeth”) is the villain, and the King's son (Malcolm) is the hero.

The film and play start at similar points. At the start of Gladiator the soldier (Gladiator) is leading the Roman armies in victory against the Germans. At the start of Macbeth the soldier (Macbeth) is playing a leading role in the Scottish army's victory over Norway.

Then comes the slightly different twist that turns them into the opposites of hero and villain. In Gladiator, when Caesar chooses his heir, he opts for the soldier rather than his son. But in Macbeth the opposite choice is made, because when the King (Duncan) chooses his heir, he opts for his son (Malcolm) rather than the soldier (Macbeth).

Thereafter, the plots are similar again. In both stories the villain, who has been spurned, kills the current king in order to claim the crown for himself.

The innocent hero is implicated in the murder, so he flees to another country (in Gladiator, the son kills Caesar and the soldier flees to Spain; in Macbeth, the soldier kills the King and the son flees to England - with his brother Macduff).

The villain, who has gained power through murder, then becomes paranoid, has people killed to protect his position (eg: Macbeth's friend Banquo is killed), and gradually goes mad.

Just as in Gladiator Commodus becomes delusional about his invincibility, so too Macbeth becomes overconfident because the witches set impossible conditions for his death ('none of woman born' can kill him, and 'Burnham wood must come to Dunsinane Hill').

Both the film Gladiator and the play Macbeth finish when the rightful heir returns from exile to reclaim the crown in a confrontation that sees the villain killed.

There are, of course, various differences in the sub-plots.

For example, in Gladiator it is Caesar who tells the soldier that he will become Caesar. In Macbeth, however, it is the three witches who tell Macbeth he will be crowned King.

Another example is that, in Gladiator, Caesar's son is not married and he becomes obsessed with establishing a line of heirs by taking his sister as his wife. However, in Macbeth, the soldier already has a wife, but the same obsession over heirs is illustrated by the 'three witches', who show him a vision of his friend Banquo's children being Kings.

In Gladiator, the villain acts alone, but in Macbeth he is aided and encouraged by his wife.

In the final scene of Gladiator, hero and villain battle each other. In Macbeth, however, the hero's brother fights the villain and kills Macbeth.

It is also worth noting that both the film Gladiator and the play Macbeth are named after the soldier – even though in Gladiator the soldier is the hero and the son is the villain, but in Macbeth the son is the hero and the soldier is the villain.

Finally, in Gladiator the story tends to focus more on the exiled hero, whereas in Macbeth the story focuses on the villain who retains power.

Any similarities between the plots of Gladiator/Macbeth and the actions of politicians, knifing each other in the back to gain political power, are not – as they say on film credits – purely coincidental. Just as in politics the one who wields the dagger never actually gains the crown (e.g.: Howe or Heseltine vs. Thatcher), so too in Gladiator/Macbeth the one who kills the villain doesn't actually become king: Gladiator dies in the final confrontation and, though Malcolm claims the crown, Macbeth is killed by the brother Macduff.