Toublanc Michelet was the "brains" of the Michelet brothers, having been the only one out of them to attend Temple school, and thus the de facto leader. He was 14 when he started his "career" as a killer.
The brothers were in Oxenfurt when they were approached by Rience to kill a supposedly ordinary man that nobody would miss, for 100 gold. Knowing something was amiss, Toublanc demanded 200 instead and Rience readily agreed, making him even more uneasy over who this person really was. He soon found out when he went with Rience to confront the man, Geralt, and the brothers began to fight while Rience ran off. Near the end of the short fight, he saw Geralt's eyes and realized he was a witcher.
After Geralt had incapacitated all four brothers and ran off after Rience, Philippa Eilhart approached and softly talked to Toublanc as he laid dying, asking him to reveal all he knew of Rience. She then took out a small stiletto and painlessly finished him off so he couldn't reveal anything to the others.