Dr Doom glimpses into the future and sees the being Onslaught, whose power Doom deems “invincible”. Doom wants to learn how that power was formed. He wonders if there is a connection between Onslaught and Magneto as Onslaught resembles Magneto in appearance. And he intends to travel through time “to pry the secrets of Onslaught’s creation from one of Magneto’s future selves”.
He travels back to when the original X-Men were still teenagers and inexperienced in dealing with Magneto. Doom instructs the Seer to “commit [Magneto’s] bio-signature to memory” so he can trace Magneto as he jumps through time.
The next time jump takes him to the Savage Land where Magneto fakes his own death. Doom moves on from this time onto the next.
Doom next sees Magneto facing “a new breed of X-Men”. While the X-Men are busy dealing with Magneto, Phoenix discovers Doom and the Seer and flies off in their direction to investigate. She is about to disable Doom’s “chronometer” when Beast is flung into her. Doom and the Seer seize the opportunity to escape.
They end up in the 21st century and see Manhattan in ruins. They are chased by a Sentinel which is promptly destroyed by Doom. Doom heads off to find tools and parts to “fix the damaged cloaking device” of his travelling platform.
When the platform is fixed, Doom and the Seer continue their search for Onslaught. The Seer briefly connects with the mind of Onslaught, and is disoriented, sending them too far back into the past. But the Seer discovers that “the secret behind Onslaught’s creation may be locked inside the head of Professor Charles Xavier” instead. Doom now sets off in search of Xavier.
Peering into the mind of Xavier, they see Xavier tormented by the death of Thunderbird and the corruption of his student Jean by the Dark Phoenix. Doom presses on, tracing Xavier’s journey to when a dying Xavier bequeaths his school to Magneto and goes to live with the Shi’ar. This leaves Doom confused as to how Xavier could become Onslaught. They return to seeking out Magneto.
Doom encounters present day Magneto. The two battle but Doom quickly escapes into the time stream.
His next destination is Avalon, where Xavier and Magneto are battling to the death on the Astral Plane. Xavier cannot forgive Magneto for killing too many innocent people and wants to make sure Magneto is never able to kill again. This act unleashes “the dark mass” inside Magneto, which merges with Xavier, forming Onslaught.
The power is too much for the time-travelling Doom and the Seer to handle, and they are thrown back to their own time. Having found the knowledge he sought, Doom kills the Seer protect the secret of the power of Onslaught.