[1] Loosely adapted from Arthurian legend, the plot takes place after the death of King Arthur, with some contradictions to the original story.

Almost all of those he knew have died; Lord Weston (Garwin Sanford) runs the kingdom and the Holy Grail has departed from the castle, but Merlin's protective enchantments have held invaders in check.

A young thief named Jack (John Reardon) and his tagalong pig Sir Snout stowaway in a cart entering Camelot, angering its driver Squire Brian.

Yvonne enters and while Jack hides, Master Graham (Christopher Jacot), a local blacksmith whom she loves, visits her.

Merlin confronts Yvonne (who is to be married to Lord Weston when the Grail returns) and her guardian Master Burton (Andrew Jackson).

Barbarians threaten Camelot's door, and knights including Brian want to use an enchanted cave in order to surprise the invaders, who they think are building a dam to drown the kingdom.

In the meantime, the barbarians directed by the Lady of the Lake enter the passage and breach Camelot's walls, which are vulnerable from the inside.

Yvonne's parents presented her as Gawain's kin but this ruse is discovered when she begs Jack to explore her past through visions.

Through these it is discovered that Master Burton and Lord Weston had oppressed the surrounding peoples with taxes, unfair trade, and devious agreements.

In the meantime, Burton hopes to betroth Yvonne to a Scottish king and indenture the remaining citizens of Camelot to that lord for personal gain.

During the reconstruction, Sir Snout tells Jack to speak the name of the land of the dead (Tartarus) in order to see his father.