3x12 - Star Wars: The Clone Wars

Troubled by Asajj Ventress' growing prowess with the dark side of the Force, Darth Sidious commands Count Dooku to eliminate her. But Ventress survives Dooku's assassination attempt, and the jilted former apprentice vows to take revenge, enlisting the aid of her kinswomen -- the mystical Nightsisters -- in her sinister scheme. Mother Talzin, leader of the Nightsisters, veils Asajj and her fellow assassins in a cloak of invisibility, and they infiltrate Dooku's palace on Serenno. Though they fail to kill the Count, their use of captured Jedi lightsabers leads Dooku to mistakenly believe that the Jedi have tried to kill him. Interested in protection, he requests a new apprentice from Mother Talzin.