The conspiracy against Lancelot and Guinevere is formulated by Sir Aggravayne and King Arthur one day when Aggravayne express outrage over the continued acceptance of the affair within the court. Aggravayne succeeds in stirring the King's anger, and Arthur agrees to spend the night away from his chambers so that Aggravayne and his men can catch Guinevere and Lancelot red-handed.
This conspiracy is formulated in Sir Thomas Malory's 1485 book, "Le Morte D'Arthur," in Book 20. The conspiracy succeeds in that Guinevere is taken into custody, although Lancelot ultimately rescues her. The conflict leads to further battle, but Lancelot insists he is still ultimately loyal to King Arthur.