This is how the three knights had arrived at Orkney: King Pellinore had been chasing the questing beast, who had dived into the ocean. He had hailed a passing ship—upon which Sir Grummore and Sir Palomides had happened to be. They arrived at Flanders and were taken in by the Court, where King Pellinore had promptly fallen in love with the Queen of Flander's daughter—a stout, middle-aged woman. However, when a magic barge appeared, the three knights investigated it and were rushed away from the coast of Flanders all the way to Orkney. King Pellinore is now deeply lovesick.
King Pellinore's game with the Questing Beast led him to arguably his true goal—to meet the Queen of Flanders's daughter. However, once more the three knights are highly comedic as the only reason they enter the mysterious barge is because, as knights, they must investigate anything mysterious. This gesture illustrates the absurdity of knightly expectations and deflates idealized chivalry.
However, Queen Morgause has set her cap at the visitors. The four boys had seen Morgause and the three knights 'hunting a unicorn,' although the hunt was apparently unsuccessful. Gareth proposes that they hunt a unicorn because it would make their mammy notice them again.
Morgause is not simply a terrible mother, but perpetually sexually unfaithful and mistreats her children. Indeed, the boys will do anything to get her attention—even hunt and kill something wholly pure, like a unicorn.
The boys need a virgin for bait, and so they decide to take the kitchen maid Meg. Gawaine marches Meg firmly by the hair and secures her to a tree, although she is crying and begs them not to. They are armed with spears from the armory and hide in a bush to await the unicorn. Meg, meanwhile, is bawling and Gareth tries to comfort her. The four decide not to kill the unicorn when it comes, but to capture it and bring it home.
The way in which the boys decide to hunt for a unicorn is described as something darkly comedic—they do not understand how one goes about it and so everything appears mismanaged and cruel.
When the unicorn arrives, it holds them all spellbound with its beauty. It is pure white, with sad, tragic eyes. The unicorn lays its head in Meg's lap. Suddenly, Agravaine is running towards the unicorn with his spear raised, and begins to jab it fiercely. Blood spurts violently. At last, the creature lies still. The others stand around frozen. "What have you done?" Gareth cries.
Agravaine's instinctive reaction to the unicorn's beauty reveals something deeply perverse in his nature—almost as though his feelings of admiration are too much for him to bear. This intensity of feeling will carry through to his later treatment of his mother and Sir Lancelot.
They do not know what to do, but suddenly the wonder of their achievement dawns over them all. They decide they must take its head home to show their mother. Meg, meanwhile, quickly runs off sobbing, closely followed by Gareth. The three remaining boys begin to hack and cut, but do not know what they are doing. They begin to cry and sweat. The head is too heavy for them to lift themselves and so they take it in turns to drag it. When they get to the castle, the prop the mangled head on a bench outside their mother's door. However, on walking past it, Queen Morgause is so distracted by Sir Grummore that she sees neither the head, nor her children.
The boys' treatment of the unicorn is dark, disgusting and deeply tragic. They act cruelly, but it is as if they know no other way to treat other creatures or people. Further, ultimately their effort—which destroyed a beautiful and innocent creature—has no effect as Morgause does not even notice the unicorn's head. Killing and the destruction of the innocent does not fill the holes caused by cruelty.