It is 13th century England. King John (Gerald Flood) is visiting the castle stronghold of Sir Ranulf Fitzwilliam (Frank Windsor).
Ranulf's personal fortune has dwindled away, freely donated to the King to help fund the Crusade.
While staying with Ranulf, the King's greed is criticised by the baron's head-strong son, Hugh (Christopher Villiers).
As a result, Hugh is challenged to a duel by the monarch's enigmatic French knight-at-arms, Sir Giles Estram (Anthony Ainley), a duel the young Englishman has little hope of surviving.
When the TARDIS materialises and disturbs the joust, the [fifth] Doctor's party are proclaimed friendly demons by the King, who seems strangely interested in their “blue engine”.
Before long the Doctor (Peter Davison) becomes embroiled in court politics, and he realises there is far more to the situation than a simple battle of honour between nobles.
Also starring Janet Fielding as Tegan, Mark Strickland as Vislor, Isla Blair as Isabella, and Michael J Jackson as Sir Geoffrey de Lacey.
Written by Terence Dudley
Producer John Nathan-Turner
Director Tony Virgo
49 minutes approx
Originally transmitted on 15 and 16 March 1983 in two episodes