The devout king Titurel has received two wondrous relics from the Angels, the Holy Grail (the cup from which Christ drank at the Last Supper and in which his blood was caught when he was crucified) and the spear with which his side was pierced. They are kept in the Castle of the Grail. Titurel has founded a Brotherhood of Knights who, miraculously strengthened by the relics, ride out into the world to help those in distress. The knight Klingsor tried to gain acceptance into the Brotherhood, but could not fulfil the law of chastity and so castrated himself in order to kill off his lustful desires. Titurel turned him away, and in revenge Klingsor transformed part of the surrounding wilderness into a magic castle and garden. Here he has created bewitching young maidens whose purpose is to seduce the knights, and he ultimately hopes to gain possession of the Grail. Amfortas, having taken over as king of the Grail from his father Titurel, sees that an increasing number of knights are falling under Klingsor´s power and so leaves to do battle with the evil magician, armed with the sacred spear. However, he is seduced by a mysterious maiden. Klingsor seizes the spear and inflicts a wound in Amfortas´ side. This wound will not close, and the king is left in agony.
Act One – Autumn
A clearing near the Castle of the Grail. Gurnemanz, an elderly knight, rouses the squires from morning prayer and instructs them to prepare for the king´s daily bath in the Holy Lake. A woman comes riding by in a great hurry. It is Kundry, enigmatic messenger of the knights of the Grail. She selflessly undergoes tribulation to serve the Brotherhood, yet always remains abrupt and cold. She has brought a balsam from afar in an attempt to heal the wounded Amfortas, and falls to the ground exhausted. The king is borne in on a litter. He has spent another night in great pain; a medicinal herb brought to him by the knight Gawain has proved to be ineffective. He now wants to try the balsam procured by Kundry, but she remarks with despairing scorn that this too will be of no use.
The king is carried to the lake. The squires, who regard Kundry with apprehension and suspicion, call her a heathen and a sorceress, but Gurnemanz comes to the help of the "wild woman", reminding the squires of her devoted services to the Grail. The squires suggest that she be sent off to recover the missing spear, but Gurnemanz says that only a hero chosen by God may perform this task. He tells of the building of the Castle of the Grail by Titurel, of Klingsor´s repudiation and revenge, of the loss of the spear and Amfortas´ wound, and of the divine prophecy that only a "pure fool", enlightened through compassion, can save the king.
Suddenly, raised voices are heard from the direction of the lake. A youth has fired an arrow at a swan circling above the water. The knights bring the dead bird and the wrongdoer to Gurnemanz, who chastises the naive youth. He is ashamed of what he has done and breaks his bow. The stranger is Parsifal, who knows neither his own name nor anything of his parents. He knows only that his mother is called "Herzeleide" (Heart´s sorrow). Kundry explains that he is the son of Gamuret who was killed in battle. Herzeleide had wanted to keep her son from becoming a knight, and so had brought him up in a lonely wood. One day, however, Parsifal saw two knights on horseback. He went after them, leaving behind his mother who later died of a broken heart. Gurnemanz believes that this is the "pure fool" of the prophecy. At this point Kundry falls asleep as if overcome by some invisible power, and Gurnemanz takes the young man to the Castle of the Grail.
The knights gather in the hall of the Castle for the ceremony of the unveiling of the Grail. Amfortas is brought in. Titurel´s voice is heard, as if from the grave. He is kept alive by regularly beholding the Grail, and bids his son carry out his office. Amfortas tells of the agony to which he must return after seeing the Grail, and beseeches his father to unveil the Grail himself. However, Titurel and the knights insist that the form of the ceremony be strictly adhered to. The Grail is solemnly unveiled. The blood of Christ glows with a wondrous light and the knights partake of the Lord´s supper. Amfortas is carried away, overcome once more by terrible pain from his incurable wound. Parsifal has watched the proceedings in complete silence. Gurnemanz assumes that he was wrong in believing Parsifal to be the promised redeemer and angrily dismisses the youth. A voice from on high repeats the prophecy.
Act Two – Winter
Sitting in his tower, Klingsor looks into a magic mirror and watches Parsifal approach; in order to rob the youth of his purity, he conjures up Kundry, who is in a trance-like state under his command. She had mocked Christ as he hung dying on the cross, and was condemned to live forever, carrying out her sentence as both the penitent servant of the Grail and a seductress under Klingsor´s power. She longs for death and redemption. These can be brought only by a man who is able to resist her, but as yet all have succumbed to her charms, including Amfortas himself. She mocks Klingsor´s enforced "chastity" and at first refuses to bring ruin on the approaching Parsifal, but she is powerless to resist her master´s command. When Parsifal reaches the castle, Klingsor sends out the renegade knights of the Grail to meet him, but the young man routs them all and descends into the garden.
There he meets the Flower Maidens, Klingsor´s creations, but he is not distracted by their childish teasing. Kundry approaches, transformed into a woman of magnificent beauty, and calls the young man by his name for the first time. She dismisses the Flower Maidens and tells Parsifal about his mother´s death. She offers the penitent and guilt-conscious Parsifal "as a last token of mother´s blessing the first kiss of love" in order to comfort him. Clasped in her arms Parsifal suddenly realises how tragedy befell Amfortas; he even thinks he can feel the pain caused by the spear wound. As foretold in the prophecy, "compassion" has enlightened him, but he remains "pure" for he pushes Kundry aside. She tells him of the curse and of her endless quest for redemption, which she hopes to find in Parsifal´s embrace. Parsifal, however, refuses to succumb and, having realised that it is he himself who has been chosen to save the world of the Grail, instead asks her to show him the way to Amfortas. Kundry curses him, saying that he shall never find the way, and calls on Klingsor for help. Klingsor appears, and hurls the stolen spear at Parsifal. But the relic cannot be used as a weapon against Parsifal, and it comes to rest in the air above his head. Parsifal seizes hold of it and makes the sign of the cross, whereupon Klingsor´s castle and garden vanish. Parsifal sets out for the Grail.
Act Three – Spring
It is the morning of Good Friday. Gurnemanz, who is now living as a hermit in a wood, finds Kundry in the forest undergrowth. She is nearly dead, but slowly she comes to her senses. When she realises where she is she begins to perform her tasks without saying a word. Gurnemanz is astounded to see that she has changed into a quiet and humble creature. An unknown knight suddenly appears, dressed in full armour. When Gurnemanz hints that this apparel is not appropriate on a Holy Day, the stranger lifts his visor. It is Parsifal who, after a long period of wandering, is finally on his way to the Castle of the Grail. Gurnemanz joyfully recognises the spear and hails Parsifal as the redeemer, explaining that since the last unveiling ceremony Amfortas has refused to reveal the Grail and has thus brought about the impoverishment of the Brotherhood and the death of Titurel. However, Amfortas is now repentant at what he has done and has decided to carry out his office at the old king´s funeral. Kundry washes Parsifal´s feet and dries them with her hair. Using water from the holy stream Gurnemanz washes all guilt from Parsifal´s head and then anoints him new king of the Grail. His first task as king is to baptise Kundry. Parsifal remarks on the beauty of the meadows which are bedecked with spring flowers. Gurnemanz explains the "Good Friday magic", which causes even the natural world to rejoice at Christ´s redemption of man. The midday bell is heard, announcing the funeral ceremony at the Castle of the Grail. Parsifal takes up the spear and follows Gurnemanz and Kundry.
The knights of the Grail assemble in the Great Hall. Shaken and penitent, Amfortas beseeches his dead father to intercede with God on his behalf. The knights press him to reveal the Grail, but he refuses and asks them to kill him instead. At this point Parsifal enters and closes Amfortas´ wound with a touch of the spear. A white dove descends from on high and hovers above Parsifal´s head. Kundry has found redemption.