With Princess Adda of Temeria he planned to take over the nation while her father Foltest was absent. They made many fake edicts to make their position stronger and eliminate all political opponents. Roderick de Wett tried to arrest Thaler for refusing to give up his position in Temerian Secret Service as he recognised the edicts were fake.
Geralt, Triss and Leavarden had a meeting with Siegfired or Yeavin to ask for help against Salamandra. Roderick de Wett tried to arrest them all but he failed as they teleported.
Roderick de Wett cursed Adda to discredit Folest and weaken his position. He also worked with Salamadra for power and profits, but when Geralt discovered it, he killed him in combat. However Jacques de Aldersberg commented that Roderick de Wett was always useless to him.
The Witcher 2: Assassin of Kings
The Witcher 3: Wild Hunt