He took a contract on a leshen that terrorized the village of Honorton in Velen. After the killing, Gaetan brought the leshen's head to the ealdorman who refused to pay the agreed upon sum. Instead, he offered Gaetan twelve crowns, a sum which would only barely cover the potion ingredients used by the witcher. After Gaetan showed his displeasure, the ealdorman and at least two other villagers led Gaetan into a barn, claiming they had "hidden gold" to give him as payment. However, it proved to be an attempt to murder the witcher. While one of them distracted the witcher by constantly chattering, another one tried to stab him from behind with a pitchfork.
Despite taking Gaetan by complete surprise, the attempt was unsuccessful and they managed only to gravely wound him. The combination of great pain, shock and anger caused the witcher to initiate a killing spree, slaying both his attackers and the entire village except for a little girl called Millie. In the end, nine people were dead. Two of the attackers (the ealdorman and the one with the pitchfork) can be discovered in the barn, two others (presumably two other attackers) right before it. The bodies of the remaining villagers are scattered around the village.
The massacre is later discovered by Geralt of Rivia who was interested in the Leshen contract. While uncovering the secret behind the massacre, Geralt finds a medallion of the Cat School which the ealdorman had managed to rip off before his death. Thanks to the little girl that was the sole survivor, Geralt managed to eventually track down the Cat witcher who was recovering from his grave injuries not far from the village.
Here, Geralt presents Gaetan the witcher medaillon he found. Geatan will then tell the fellow witcher the whole story behind the massacre, including both a confession and regret for his actions. There are also subtle hints evident that Geatan had lost his temper in a similar fashion at least once. Geralt can then choose what to do with his colleague. However, the choice is a tough one.
Geralt can choose to ignore that the villagers attacked Geatan first and argue that, even if Gaetan can be sympathised with and he acted in self-defence against the attackers, his killing of presumably innocent villagers can not be justified.
Furthermore, Geralt could argue that Gaetan would be a risk for other people should his temper get the best of him once more. Gaetan will then be forced to duel Geralt, a fight in which the former will eventually be killed.Otherwise, Geralt can choose to deem himself neither adequate nor in the position to judge Gaetan for what happened in the village. After all, the villagers didn't keep their end of the bargain and tried to murder the witcher, even though the witcher responded with an overreaching act of violence. So which one of these two factions is at fault, Geralt can argue, can not be judged nor will it be judged by him.
Geralt then tells Gaetan that he himself is often referred to as the Butcher of Blaviken and that sometimes "heads just roll", indicating that he neither absolves nor condemns the other witcher for what he did. Besides that, one could argue that enough blood has been shed under already tragic circumstances, thus it would not be ethical to kill another person that can not be regarded as the initial aggressor in any way. Should Geralt choose to not judge Gaetan, the Cat witcher shows his gratitude by letting Geralt take the sword from his nearby hideout.
- If you approach Gaetan while wearing the Cat School Witcher Gear, he will comment on it before you engage him in conversation. Saying "Well well, what have we here? Feline armor, wolf's head medallion - a crossbreed?".
- In the Hearts of Stone expansion, during the secondary quest Avid Collector, Marcus T.K. Hodgson may award Geralt with Gaetan's conserved shaelmaar trophy, which he had apparently given to Hodgson as collateral for a purchase.
- In Gaetan's hideout he has a wall of trophies he collected which Geralt wonders why he still has them and believes he may have been cheated of his reward in the past and kept them as mementos.