While Barnabas was hunting in Silithus he received word that his niece, Jillian Grell was murdered by the Scarlet Crusade at her farm. After flying from Silithus to Undercity, he accidentally bumped into Reynah Firecaster, who was not looking where she was going, and the two had an argument, threatening to kill each other if they ran into each other again. Barnabas left Undercity and began hunting down scattered Scarlets he found around Tirisfal Glades until he again ran into Reynah. Before the two killed each other, they came to an understanding that they both were hunting the same targets and decided that, until they killed the Scarlet leader Renee Lauer, they would work together.
The two attacked attacked the Scarlet camp and managed to capture Renee. However the two began arguing over who would deal the killing blow, allowing Renee's allies to arrive and incapacitate both of them. Before their execution Barnabas and Reynah told the Scarlets they vowed vengeance over the deaths of their loved ones and asked Renee why would she kill innocents. When Renee responded that the Forsaken and the blood elves were a disease in infesting human lands Reynah attacked the surrounding Scarlets with her fire magic, until they were cornered and injured explosives. Barnabas was permanently killed by decapitation, while Reynah's neck was snapped. Moments later, Forsaken lead by Sylvanas Windrunner and Varimathras killed the entire camp, and raised Renee Lauer as one of the undead.