Altar of Mortis ( episode ) " Altar of Mortis " is the sixteenth episode of the ' . It aired on February 4 , 2011 . Official description . " " Before the Jedi can leave Mortis , the Son takes Ahsoka captive in an attempt to entice Anakin into joining him to use their combined strength to overpower his Father and Sister . To this end , the Son casts Ahsoka under the spell of the dark side . " " Meanwhile , the Father attempts to stave off a disastrous showdown between his children and maintain the Force ' s increasingly precarious balance on the planet . Fearing that the Son may be unstoppable , the Daughter does the forbidden by taking Obi - Wan Kenobi to the Altar of Mortis , wherein is kept the Dagger of Mortis , a weapon capable of killing a Force wielder . The Son steals the weapon , and attempts to use it against his Father to steal his power and end his rule , but the Daughter sacrifices herself , placing herself in front of the blade . " " Plot summary . As Anakin , Obi - Wan and Ahsoka are about to leave Mortis ' world , Anakin , while resting from this morning ' s ordeal , has a disturbing dream in which he finds himself back in the planet . What appears to be a mirror image of himself approaches him , only to reveal itself as Son , who asks Anakin to join him on the dark side of the Force and restore peace and balance in the galaxy . When Anakin refuses and turns away , Son turns into a monster and attacks him , jerking him awake . Ahsoka walks into the room meanwhile . Suddenly the ship tilts and starts rocking wildly . But just as Anakin prepares to join Obi - Wan at the controls , Son suddenly appears behind them , kidnaps Ahsoka and jumps out of the shuttle . He shifts into his gargoyle form and flies off with Ahsoka in his talons . Running into the cockpit , Anakin took over and chased after Son into a canyon of mist - shrouded rock spires , but Son puts on a burst of speed and disappears into the mist . Anakin flies even faster and instead comes upon a strange tower supporting a huge glowing sphere . Just narrowly avoiding a collision with the structure , Anakin is unable to control the shuttle , and it crash - lands back on the planet , in an area dominated by darkness . In the distance they can both clearly see the tower with the glowing sphere on top of it ; Obi - Wan assumes that ' s where the Son had Ahsoka . Claiming it was his fault the Son had taken Ahsoka , Anakin prepares to go for the tower , but Obi - Wan holds him back , desperately cautioning him not to let himself get lured into an obvious trap lest it would yield catastrophic consequences . He suggest consulting Father about how to proceed , but Anakin nevertheless leaves for the tower . While Obi - Wan ponders how to reach the Father in the first place , he suddenly finds himself very close to the monastery . Inside her prison cell within the tower , Ahsoka tries to free herself , she hears a voice and then she finds herself in the company of a creature which addresses her innermost doubts and fears . It questions where her Master is and claims that he won ' t come . Ahsoka snaps that Anakin will rescue her . It releases her from her chains . It tries to convince her to forget her Master , but seeing that she will not willingly turn , it bites her in the arm . Clutching her arm , Ahsoka collapses on the floor , the creature morphs back into its true form , the Son ; his bite now infects Ahsoka with the Dark Side of the Force , and she undergoes a horrifying change . Son thereafter joins his father and sister ; Father expresses worry about his son ' s descent into the Dark Side and implores him to let go of it , whereupon Son lets loose with his anger and blasts Father with Force lightning just as Obi - Wan arrives . Daughter who had heard the fight ran to help her father . Upon Father ' s sickbed , Obi - Wan implores Daughter to assist him in stopping Son before he escapes the planet , but Daughter , saying it is not Son ' s fault as that is his nature , refuses to raise her hand against her brother . Upon his suggestion that she and Anakin should combine their powers to stop him , Daughter instead leads him to a cavern which contains an altar holding a blade formed by pure Force , which Obi - Wan is meant to wield against her brother . Meanwhile , Anakin manages to scale Son ' s tower and finds Ahsoka waiting for him . Unfortunately , he discovers that she is corrupted by the Dark Side ; Son infused her with part of his own soul , bringing out her insecurities and resentments along with her other more aggressive tendencies . She leaves Anakin a message : either join the Son or he kills Ahsoka . When Anakin dismisses the threat she ignites her lightsaber and viciously attacks him . Obi - Wan and Daughter confront Son in his inner sanctum , but he manages to separate them by directing Obi - Wan into assisting Anakin . As Obi - Wan arrives Ahsoka turns and activates her shoto and begins to attack them both . During the fight Anakin turns to Obi - Wan knowing that they could not defend themselves for long without either harming Ahsoka or her eliminating them . Obi - Wan then pulls out the Mortis Dagger he received from the cave altar and suggests they free Ahsoka from the Son ' s influence . Ahsoka , angered and knowing exactly what they have , continues fighting the Jedi to get the blade from Obi - Wan . Meanwhile , Son and Daughter began a duel using their Force powers to overpower each other . They later began shifting in and out of their beast forms . Soon however , they were interrupted by the recovered Father , who hurls them among the Jedi . Son turns his anger against his father , who is unable to prevail against him in his still - weakened state . During the whole ordeal , Ahsoka got up and smirked as the Son uses lightning on the Father . Obi - Wan throws the dagger to Anakin , but Ahsoka dives , catches in mid - air , then runs up to the Son and hands it to him . Son thanks her and claims she is no longer useful to him anymore . Son taps her on the forehead , removing her life force and therefore killing her instantly . Her lifeless body collapses to the floor as her lightsaber rolls out of her limp hand . Enraged , Anakin lunges at the son , but is repelled by the force . Son then turns and prepares to plunge the dagger into his father , but Daughter steps in front of her father , taking the blade instead , she is mortally wounded . Screaming with sudden anguish , Son flees the scene as Anakin rushes to Ahsoka ' s side , only to find her eyes completely rolled back . With Daughter dying , the balance of the Force is upset , and the planet begins to descend into eternal darkness . Anakin , kneeling beside Ahsoka ' s lifeless body , begs Father to help her . Daughter uses Anakin as a conduit to channel the last of her life force into Ahsoka , removing the darkness within her , bringing her back to life . Ahsoka awakens , weak , but alive . Anakin hugs his apprentice and asks if she is alright , only to find out that she remembers nothing of what had happened to her . Father implores the Jedi to leave before Son can take their ship to escape the planet , and warns them that with the balance disrupted , the Dark Side and the Sith will gain the upper hand in the galaxy . Unable to do anything else , the three Jedi leave the mournful Father by the side of his daughter .