Yadeth was a Wizard and the leader of the Black Hand in the Year 425. The wizard first became known when he commanded an attack on the city of Mirith sometime in that year. The forces of Mirith beat back the invasion, but at the battle's end, Yadeth appeared in front of King Galandir and the heroes of the day. Yadeth claimed that he had kidnapped the King's sister and heir to the throne, the Duchess Tirana. He told the Mirithians that he would return Tirana to them in exchange for Mirith's piece of the Curio. However, Yadeth only gave them three days to complete the task. The Royal Guard Zexe decided that the only good way to find Yadeth would be through the help of a user of Black Magic. Zexe went off to search for the Royal Mage Beleth, who was nowhere to be found.
When news of the attack reached Mayor Palmer of Lerilin, he fled his town. Palmer had been attempting to discover the secret location of the Black Hand's headquarters, and he feared that the Black Hand would attack Lerilin to stop him. In his absence, Palmer continued to seek for the Hand's base of operations.
Meanwhile, Yadeth launched a small-scale assault on Mirith once more. Although the attack was quickly repelled, it is believed that it was just a reminder and a show of power on the wizard's part.
Then, on the eve of the third day, Yadeth summoned an army of Rust Beasts, Poison Beasts and Lava Spiders to attack Mirith yet again. The creatures were brought down after a long fight. The warriors of Mirith agreed that they had to find Yadeth right away. With Beleth still missing, the heroes decided to seek out the wizard Seth instead. Seth was found in Brigobaen, and although he was reluctant to become involved with the royalty, he agreed to help because disaster would strike if Yadeth acquired the Curio. Although Seth had more than enough strength required to cast the spell, he had never met Tirana or Yadeth. Because of this, the spell wouldn't work. At that moment, Beleth revealed himself. The two wizards were able to complete the spell and find Yadeth's location: Port Gast.
The heroes left the exhausted wizards and returned to Mirith, where King Galandir organized an army and sent them off. Tirana was found tied up in a crude shelter near the port. She was freed without trouble. Then Yadeth appeared and the battle began. Summoning hoards of elementals at a time, Yadeth managed to prevent the Mirithians from harming him. According to a previously made plan, the Mirithians slowly but surely pushed Yadeth to the nearby seas. Eventually Yadeth was standing on a raft in the ocean, and he used his Black Magic to summon a wave of deadly Sea Serpents.
Nita, the princess of the Mhara, was waiting for Yadeth in the ocean. She spoke some words in the Mhara tongue, causing the serpents to turn against and devour Yadeth. The warriors and Tirana returned victorious to Mirith. However, Yadeth's influence was far from over.
Not long after Yadeth's death, a group of adventurers found the Twins guarding special structures inside the Tree Maze. These structures became known as the Poison Forges. These Forges were dumping massive amounts of poison into the waters, endangering all creatures that resided in the water, including the Mhara. Thanks to a public letter written by Palmer during his flight from Lerilin, it was revealed that Yadeth had been poisoning the waters even before his first attack on Mirith and the subsequent kidnapping of Tirana. After some time passed, the Poison Forges were eventually destroyed. Yet Yadeth was to play a major role in events yet again. His death led his wife to seek vengeance on Mirith. Her name was Elefin, and she became the new leader of the Black Hand after her husband's death.