Beroun first appears as a Saxon ally of Morgana. He helps her in her hunt for Alator, and then brings her the box containing the Nathair. Later on, he finds the letter Finna sent to Alator and organises his men for another hunt. He shoots Merlin with a crossbow and severely wounds him, but is thrown back by Finna using magic. He comments that the bodies of his allies who Finna killed bear no wounds. Beroun leads the attack on the ruined castle, and is seen looking around for treasure shortly after Finna's death. Morgana tells him to burn Finna's body and get the horses ready. Beroun presumably appears in later episodes, as he survives (The Kindness of Strangers).
Beroun later appears in Morgana's hideout, after the Battle of Camlann, standing side by side with two other Saxons. Morgana appears to suffocate one man standing beside him, and he appears shocked but still loyal to Morgana. He later meets Merlin out on his horse with Arthur, and appears to show compassion, as Merlin tells him they have been attacked by Camelot knights. Beroun questions if they were really Camelot knights, then pushed Merlin aside to inspect Arthur, who is hidden by a rag, and discovers his sword, to which Merlin attacks him and his colleague, killing them.
Little was known about Beroun, and how unquestioned his loyalty was to Morgana. His own personal aims were unknown and why he allied with Morgana and the Saxons. When Morgana choked one of his colleagues, he appeared to understand Morgana's anger and continued the search, even after telling her they were hopeless.