After Arthur finds out about Guinevere's betrayal, he goes to fight Morgan and his knights. In the battle, he kills his upstart son, but is mortally wounded. His last loyal knight, Sir Bedivere, stays with his king to the bitter end.
The king gives his knight his sword, and tells him to go to the lake where he got it from, and throw it in, then come back and tell him what he saw. The knight goes to the lake, but hides the sword in some bulrushes and comes and tells the king he saw it falling into the water.
The king knows he's lying, and asks him to go back and throw the sword in this time. The knight goes back to the pond, but again doesn't throw in the sword. The king tells him he would kill him if he doesn't, and Sir Bedivere throws in the sword. To his surprise, a hand comes out of the lake and catches the sword, then it sinks back in.
The knight goes back to his king, who now knows he threw in the sword, and Arthur asks Bedivere to help him go to the lake. There, a black boat comes to the bank and takes King Arthur away. Sir Bedivere goes to the top of a hill, and watches the boat take his king away.