During this mission Dooku searched for a new ally with enough power to defeat a Jedi . In 22 BBY he went to the Cauldron (a combat ring on the planet Rattatak) to find a assassin for the Separatists. He saw many gladiators fighting but the warrior Asajj Ventress dominated them all. After she introduced herself to Dooku and said she was a Sith Dooku challenged her in a combat and defeated her. He used Force Lightning on her and knocked her unconscious. After she waked up she fought him again. Finally Dooku chopped Ventress' lightsabers in half and won the duel.
Dooku was very impressed with her skills and he presented her to Darth Sidious. He gave her an important mission: she must assassinate Anakin Skywalker. After she received the lightsabers of Komari Vosa, she left in a Fanblade starfighter to kill Skywalker.