The giant of the Victorian era was Alfred, Lord Tennyson, whose Idylls of the King constitute an epic in poem form. As such, Tennyson is hearkening back to the beginnings of Arthurian literature.

Tennyson himself began with The Lady of Shalott, about a woman who loves Sir Lancelot but cannot have him. He would later revisit this story in Lancelot and Elaine. The tale itself was based on a medival Italian novelette, Donna di Scalotta. He moved to Sir Galahad and then Morte d'Arthur in completing his early phase of exploring the Matter of Britain.

Merlin and Vivien begin their story in Broceliande Forest. Vivien is here presented as the paramour of King Mark of Cornwall, who sent her to Camelot so she could uncover Lancelot's and Guinevere's affair and expose its spreading effects on the morality of the Round Table knights. Her initial strategy, that of being made a lady-in-waiting to Guinevere, is successful; but she fails to convince Arthur of how much he needs her. She sets her sights on Merlin. The old man, depressed, sails away in a boat and lands in Brittany, in the Broceliande Forest. Vivien has followed him there and now is trying to get him to reveal her the secret of the locking-away charm. She tries all manner of tricks, including appealing to his paternal instincts and his hedonistic instincts, but nothing works. Finally, exhausted, Merlin relents and falls asleep. The charm secret hers, Vivien locks Merlin away.

Lancelot and Elaine introduces the idea of the nine valuable jewels, one of which Arthur would give to the winner of the annual tournament. Lancelot, of course, won all nine, although the last took a little longer to deliver. It seems that Lancelot had disguised himself in the last battle, wearing unfamiliar attire and sporting the favor of the young Elaine of Astolat, at whose father's castle he had stayed while on his way to the tournament. Despite the disguise, Lancelot wins, although he is cast out for being a pretender. Arthur charges Gawain with delivering the diamond to the winner; he finds his way to Astolat, sees Lancelot's shield with Elaine, and leaves the diamond with her. He returns to Camelot and tells everyone he can find that Lancelot really loves Elaine. She, meanwhile, has found Lancelot, who was wounded in a skirmish after the tournament, and is nursing him back to health. He cannot shake his love for the queen,, however, and leaves Elaine alone. Despondent, she soon dies. Lancelot presents the nine diamonds to Guinevere (for Elaine had given him the last one), but she accuses him of infidelity to her and throws the diamonds out the window. Lancelot looks down at the river below and sees the barge bearing Elaine's body. In it is a note that blames Lancelot for her death. This poem ends very sadly, with the twin images of Elaine's barge and Lancelot's self-pity.

The Holy Grail opens with a very old Percivale recounting the Grail tale to a monk named Ambrosius. The tale tells of Galahad's sitting in the Siege Perilous, which revealed a vision of the Grail. Most of the knights took an oath to seek the Grail; Arthur was not there, so he did not take such a vow, and he chastised his knights for binding themselves so. The tale takes the familiar turn of having Bors, Percivale, and Galahad see the Grail, the latter two sharing a vision in a chapel. Bors returns to Camelot, in this tale accompanied by Percivale, to find a broken court: Lancelot is consumed by his vision, which availed him an out-of-focus glimpse; Arthur is beside himself with woe for the loss of so many knights. The poem ends abruptly and sadly.

Guinevere sees the evil plans of Modred and Vivien come to fruition. Modred attempts to catch Lancelot and Guinevere in the act of adultery. In a flash, Lancelot escapes and flees to France and Guinevere takes refuge in the nunnery at Almesbury. She remains there and hears the news that Arthur is making war on Lancelot while leaving Modred behind as regent and that Modred has seized the crown and is preparing for Arthur's attack. Arthur himself comes to Guinevere in the abbey, saying "I did not come to curse thee." Nonetheless, she feels remorse at what she has done. When he leaves, she realizes that she still loves him. She hears of his passing and grieves heavily.

The story of The Passing of Arthur is told by Bedivere, the last survivor of the Round Table. He speaks of Arthur's wondering whether God has forsaken him and of his conversation with the ghost of Gawain and of his determination to follow the path fate had ordained for him. The last battle takes place in a veiling mist, in which one could easily believe that the knight right next to you was your enemy, not your friend. The fateful combat of Arthur and Modred comes after the battle is over. Bedivere takes Arthur to a nearby chapel, and the king instructs his faithful follower to throw Excalibur into the lake outside. The sword lands in the hand of an outstretched that soon disappears beneath the surface. Arthur is carried onto a barge, to carry him to Avilion, "Where I will heal me of my grievous wound." The poem (and the saga) ends with a new spring morning, a symbol of great things to come.