The Holy Grail loosely follows the legend of King Arthur.
Arthur along with his squire Patsy recruits his Knights of the Round Table, including Sir Bedevere the Wise, Sir Lancelot the Brave, Sir Robin the Not-Quite-So-Brave-As-Sir-Lancelot and Sir Galahad the Pure.
The group is instructed by God to seek out the Holy Grail.
They are led to a castle controlled by the French where they believe the Grail is being held. After being insulted in mangled Franglais and failing to invade the castle in a Trojan Rabbit, Arthur decides that they must go their separate ways to seek out the Grail.
Concurrent to these events, in a manner of breaking the fourth wall, a modern-day historian, while describing the Arthurian legend as for a television program, is killed by a knight on horseback, triggering a police investigation.
Each of the Knights encounter various perils on their quest.
Arthur and Bedevere attempt to satisfy the strange requests of the dreaded Knights who say Ni. Sir Robin narrowly, but bravely, avoids a fight with the Three-Headed Giant. Sir Lancelot accidentally assaults a wedding party at Swamp Castle believing them to be hiding the Grail. Galahad is led by a Grail-shaped beacon to Castle Anthrax, populated by only comely women who wish to perform sexual favours for him, but is "rescued" by Lancelot.
The Knights regroup and travel to see Tim the Enchanter, who points them to caves where the location of the Grail is written on the walls. To enter the caves, the group is forced to defeat the Rabbit of Caerbannog using the Holy Hand Grenade of Antioch.
With their final destination known, the group travels to its last peril, the Bridge of Death, where each Knight is forced to answer three questions by the bridgekeeper before they can cross; Sirs Robin and Galahad fail and are thrown into the chasm below the bridge, before Arthur tricks the bridgekeeper. Lancelot becomes separated from Arthur and Bedevere, later shown arrested by modern-day police for the murder of the historian. Arthur and Bedevere travel to the Grail's castle, which they find is already occupied by the French who send them away with their insults.
They amass a large army to prepare to storm the castle, but just as they are ready to start the charge, the police arrive and stop it, arresting Arthur and Bedevere, and putting an end to the film; the search is never resolved nor are further inquiries ever held.
(Apologies to Monty Python however, there are many, many similarities where I shall leave it to readers to apply places and posters names to characters from the film as appropriate to this everlasting tale)
DK