But it soon becomes apparent to the Doctor that something is very seriously wrong. Why does John express no fear or surprise at the time-travellers' sudden appearance, and indeed welcome them as the King's Demons? And what is the true identity of Sir Gilles, the King's Champion?

Very soon the Doctor finds himself involved in a fiendish plan to alter the course of world history by one of his oldest and deadliest enemies.
 

'We sing in praise of total war; against the Saracen be abhor'

It is thirteenth century England, and King John is visiting the castle stronghold of Sir Ranulf Fitzwilliam. Ranulf's personal fortune has dwindled away, freely donated to King John to help fund the Crusade. While staying with Ranulf, the King's greed is criticised by the baron's head-strong son, Hugh. As a result, Hugh is challenged to a duel by the monarch's enigmatic French Knight-at-arms, Sir Giles Estram, a duel the young Englishman has little hope of surviving.

When the TARDIS materialises and disturbs the joust, the Doctor's party are proclaimes the friendly demons by the King, who seems strangely interested in their "blue engine". Before long the Doctor becomes embroiled in court politics, and he realises that there is far more to the situation than a simple battle of honour between nobles.

Ranulf's cousin, Sir Geoffrey de Lacey, arrives at the castle and is astonished to find the King present. He has just left His Majesty in London preparing to sign the Magna Carta, a document that will shape the future of democracy in the western world. The Doctor learns that neither the King nor Sir Giles are exactly who they claim, and their true identities involve a battle-ravaged alien planet light-years away, and one of the Doctor's oldest and deadliest enemies ...

Originally transmitted 15th March to 16th March 1983

Running time: 51 mins approx
Cover Illustration by Colin Howard

Produced by John Nathan-Turner
Directed by Tony Virgo