Arcannen Rai is a character in The Defenders of Shannara trilogy. He is a sorcerer intent on acquiring powerful magic for his own use, whether that magic be imbued in items like the Sword of Leah or innate in other people, like the wishsong.
Arcannen lives in Dark House in the Southland city of Wayford. He first comes to the attention of Paxon Leah when he uses his magic to lure Paxon's sister Chrysallin into a chance game and abduct her. Paxon tries to stop Arcannen from leaving Leah but is easily overpowered by the sorcerer, who dares Paxon to come after him.
Paxon pursues Arcannen to Wayford, taking the Sword of Leah with him. It later becomes apparent that Arcannen wanted Paxon to pursue him with the sword, so that the magic of the sword might be activated and he could claim the sword for himself. Arcannen's plan backfires when Paxon not only unlocks the sword's magic but manages to overpower the sorcerer with it and take Chrysallin back as well. Despite losing the duel, Arcannen manages to escape.
The use of magic in the battle between Paxon and sorcerer catches the attention of the Druid Order, and Paxon is summoned to Paranor by Aphenglow Elessedil, Ard Rhys of the Druids. There he is recruited to become the Blade of the Ard Rhys, a warrior sworn to protect the Druid Order.
While Paxon is away from Leah training in Paranor, Arcannen abducts Chrysallin once more and brings her back to Wayford, where the witch Mischa begins torturing Chrysallin under Arcannen's orders. Mischa uses her magic to brainwash Chrysallin into thinking she is being badly mutilated and defiled, and that the Ard Rhys of the Druids is responsible for her torture. Arcannen's plan is to imbue enough fear and hatred of Aphenglow Elessedil into Chrysallin's mind that Chrysallin would kill the Ard Rhys using the Stiehl, which Arcannen intends to provide to Chrysallin.
But Paxon and the Druid Starks go after Arcannen to rescue Chrysallin, and Grehling Cara, the fourteen-year-old son of Wayford's airfield manager, and Leofur Rai, Grehling's former nanny, have already been working to free Chrys from Mischa. Grehling and Leofur manage to get Chrysallin away from Mischa, and Paxon kills a creature of magic sent by the witch to pursue Chrysallin. A traumatized Chrysallin kills Mischa herself using the wishsong. Arcannen gets away, but not before killing Starks using the Stiehl.
Chrysallin is catatonic after using the wishsong, and Paxon takes her to Paranor. There everyone realizes that she has been tortured mentally, brainwashed into thinking that Aphenglow is responsible for her torture.
Accompanied by Leofur, Paxon returns to Wayford, ostensibly to find some clues that might help bring Chrysallin out of her traumatized state, but also to avenge Starks' death by killing Arcannen. In Wayford Leofur gains easy access to Dark House, and there Paxon and Arcannen do battle. Paxon gets the upper hand and Arcannen, realizing he is about to be overpowered, offers to give Paxon a potion that will cure Chrysallin of the effects of her torture if Paxon will let him go. Although deeply conflicted, Paxon realizes that healing is sister is more important than gaining revenge, so he agrees to the exchange. Arcannen finds the potion hidden in Mischa's former home and flees Wayford.
After Arcannen flees, Paxon, who had been developing feelings for Leofur, learns that Leofur is in fact the sorceror's estranged daughter. Back in Paranor, Paxon administers the potion to Chrysallin, who comes out of her catatonic state fully healed, not even able to remember what had been done to her.
Later, Arcannen disguises himself at the Druid ambassador Isaturin and visits the Federation's Minister of Security, Fashton Caeil. In his disguise, he kills the Minister with the Stiehl and leaves, leaving the Stiehl at the scene of the crime to pin the blame on the Druids and their weapons of magic and create discord between the Druids and the Federation. However, despite many in the populace believing that the murder was carried out by the Druids, the Federation's Prime Minister is not fooled, and he visits Aphenglow privately to exchange information. They confirm that Isaturin was in Paranor at the time of the murder and that the murderer was most likely Arcannen.
Shortly afterward, Aphenglow travels out of Paranor in her personal airship with Paxon, her young assistant Sebec, and several of the Trolls serving as Druid Guards. When they reach the Streleheim Plains, Aphenglow announces that Sebec is the traitor within the Druid Order who has been passing information and artifacts of magic to Arcannen, including the Stiehl. Sebec had even attempted to steal the crimson Elfstones. For these crimes, the Ard Rhys has the guards execute him.
Five years later, shortly after the death of the Ard Rhys, a young balladeer appears who has the use of the wishsong, a magic that belongs only to the Ohmsford family. Arcannen attempts to convince Reyn Frosch, the young man with the power of the wishsong, to ally with him, in an attempt to use Reyn's power to avenge the people of the town of Arbrox, who had given him shelter and were annihilated by the Federation.