Bayard led a delegation of the Mercian court to Camelot to meet with Uther and sign the treaty. The peace was threatened soon after when, during a celebratory feast, Merlin accused Bayard of attempting to assassinate Prince Arthur Pendragon. However, the handmaiden in Bayard's entourage who had informed Merlin of the poison was in fact the sorceress Nimueh, who was plotting to kill the young warlock, not the prince.
As was Nimueh's intent, Merlin was forced to prove his allegation by drinking from the goblet he accused Bayard of poisoning. Thus, Merlin suffered from the poison in Arthur's stead.
Bayard and his entourage were imprisoned for the attempted assassination while Gaius, Guinevere, and Arthur sought an antidote to the poison afflicting Merlin. Gaius eventually uncovered the true identity of Merlin's informant and revealed to Uther that she, and not Bayard, had poisoned the goblet. Uther released Bayard, preventing an attack on Camelot by Mercian forces, and the peace accord presumably remained in effect (The Poisoned Chalice).