This horn she sent to Arthur's court, hoping that Guenever might drink thereof and be dishonored, for her love for Lancelot was known to all but the king.
Lamorak, learning from the boy his errand, bade him bear the horn to King Mark's court, and tell the king that it was sent to prove the falseness of his lady, who loved Sir Tristram more than she did her wedded lord.
Soon afterwards, therefore, the boy appeared at Tintagil Castle, and presented King Mark the magic horn, telling him of its virtues, and all that Sir Lamorak had bidden him say.
"By my royal faith we shall try it, then!" said the king. "Not only my queen, but all the ladies of the court, shall drink of it, and we shall learn who among them has other lovers than their liege lords."
Much to their unwillingness, Queen Isolde and a hundred ladies of the court were made to drink from the magic horn, and of them all only four drank without spilling the wine.
"Now, by my knightly honor, all these false dames shall be burnt!" cried the king. "My court shall be purged of this vile stain."
"That shall they not," cried the barons. "We shall never consent that the queen and all these ladies shall be destroyed for a horn wrought by sorcery, and sent here to make mischief by as foul a sorceress and witch as the earth holds. She has always been an enemy to all true lovers and sought to do them harm, and if we meet with Morgan le Fay she will get but scant courtesy at our hands. We would much rather believe the horn false than all our ladies untrue."
But Tristram's anger was turned towards Lamorak for this affront, for he knew well what had been his purpose. And he vowed in his heart that he would yet repay him for this treacherous act.
His affection for Queen Isolde kept as warm as though the love-draught still flowed in his veins, and he sought her at every opportunity, for the two greatest joys that life held for him were to tell her of his love and hear from her lips that her love for him had never dimmed.
But his treacherous cousin Andred watched his every movement, and kept the king advised that Tristram continued his secret interviews with the queen. So an ambush of twelve knights was set, and one day, when Tristram had just paid a stolen visit to the queen, and sat in loving converse by her side, these ambushed knights broke suddenly upon him, took him prisoner, and bound him hand and foot.