|First printing||September 1998|
Planeswalker is told from the point of view of Xantcha, a Phyrexian newt rescued by Urza, in a series of flashbacks as Xantcha attempts to help Urza regain his sanity after several millennia of fighting Phyrexia.
Five years after the Sylex Blast Urza returns to Dominaria after traveling the multiverse and developing his powers as a planeswalker. Investigating Koilos, Urza is given a vision of the ancient Thran fighting Phyrexians and he discovers that the powerstone he and Mishra took was the keystone blocking the Phyrexians from returning. Urza swears vengeance on Phyrexia and vows to destroy it.
In Phyrexia, Xantcha is created as a newt in the Fourth of Nine Spheres to be a sleeper agent sent to Dominaria. Her heart is separated from her and complete obedience is drilled into her mind but Xantcha has an unusual individualism that attracts the attention of her overseer, the demon Gix, who opens her mind. When the first wave of sleepers are discovered and destroyed in Dominaria, Gix is publicly excoriated and Xantcha is sent with teams to other planes looking for artifacts for Phyrexia. Xantcha develops a hatred of Phyrexia and sabotages these missions but is discovered and is about to be executed when Urza appears and saves her, believing her to be human abducted and “emptied” by Phyrexian brainwashing. Urza waits for the Phyrexians to return from their plane, and then uses their ambulator to enter it with a constructed dragon engine. Xantcha follows him and recovers her heart from the Fourth Sphere as Urza destroys huge swaths of the plane. Seeing that Urza is killing thousands but is slowly being overwhelmed, Xantcha manages to reach the dragon engine and yells at him to planeswalk away.
Xantcha and Urza are constantly chased by Phyrexian negators throughout the multiverse. They are unable to stay on any one plane for more than a year before they are discovered. This constant chase puts Urza in an unfocused frenzy and he begins to rely on Xantcha to give him purpose and discern reality from fantasy. As they flee, Urza reveals that he is unable to return to Dominaria or the planes near it because they are encased in an impenetrable Shard. One Negator team almost kills them both, but Urza randomly planeswalks them at the last moment to Serra's Realm. There Urza recovers with the help of the plane's white planeswalker creator Serra. Urza realizes that Phyrexia is a similarly artificial plane and that the Phyrexians must have originated somewhere, and they were cast out. Urza decides to look for this first plane and allows Xantcha to accompany him after she gives him her heart to show her loyalty. Their search takes them to many planes such as Equilor and Vatraquaz. Eventually, the Shard is broken and Urza brings Xantcha to Dominaria in 3210 AR.
Years later Xantcha and Urza live in a remote cottage in the Ohran Ridge. Urza has become so obsessed with the past and his brother's corruption that he is oblivious to the present. Phyrexian sleepers have infiltrated many organizations on Dominaria and have instigated wars to weaken the local populace. Desperate to refocus Urza on the present threat of Phyrexia, Xantcha finds a man that physically resembles Mishra, a slave named Ratepe, to pretend to be Urza's brother. “Mishra’s” presence shakes Urza from his stupor and he makes plans to expose the sleepers by using mechanical “screaming” spiders that activate at the apex of the white-magic Glimmer Moon. In the process of spreading these spiders, Xantcha discovers that Gix himself is on Dominaria. Gix recognizes her and makes unsettling comments about Urza, but Xantcha barely escapes, and Urza declares that he will finish the mission himself, giving Xantcha and Ratepe a few days off. They decide to go to Koilos, and there they discover Phyrexia's secret. The Phyrexians were actually Thran that rebelled and were then cast out from Dominaria. They decide not to tell Urza before the mission is finished.
On the night of the Glimmer Moon's apex, Urza brings Xantcha and Ratepe to the city where Gix was. The Moon activates the spiders and all the nearby sleepers are affected and killed. Gix himself emerges and Urza attacks, chasing the demon all the way to Koilos. Xantcha and Ratepe watch as Urza and Gix fight a brutal battle that eventually comes down to a contest of wills embodied by a web of blue-white light between the two combatants. Xantcha and Ratepe see that Urza is losing when his powerstone eyes are slowly pulled out of his head towards Gix. They move to either side of the web and reach into the light to stop the powerstones. Gix tries to destroy them but at that moment when his focus is disturbed, the powerstones are freed and destroy the demon. Ratepe and Xantcha are lost in the explosion.
Urza awakens after the battle and calls for Xantcha before realizing both she and Ratepe are gone. He determines that he must go back into the past to the Thran but also realizes that the battle in the present needs to be fought. Urza begins to think that he will have to do it alone but remembers Xantcha's heart and realizes that he will never be alone.
The story continues in Time Streams.