A police car enters a maximum security prison, and a policeman comes out of
it and goes inside. After endless security checks, including a palm scanner
and a retina scanner, he finally reaches a glass tube that is the prison of
Cain Marko, the unstoppable Juggernaut. The policeman reveals to be
Mystique, and wakes up Cain, telling him that it's time he had a long
overdue family reunion with his brother, Charles Xavier.

In a survival camp, a man named Sgt. Hawke introduces the kids standing in
line, including the X-Men and the Brotherhood, to the harsh rules of
Ironback Survival Camp. He then tells them that Scott Summers will be their
group leader and dismisses them. The X-Men start complaining about how they
have to go through the survival training and how their only other option was
to train with Wolverine. Scott and Jean try to cheer them up, but they're
sure they won't make it. The Brotherhood isn't exactly happy either,
especially with the fact that Scott is group leader. Fred and Todd plan to
battle them in the woods, but Lance tells them it'll be better to beat them
in public.

Back in the prison, Mystique releases Cain and tells him that she'll help
him escape. He asks her who she is, and she tells him that she has a deal
for him – his early release, in exchange to Cerebro. As for Xavier's fate,
she says, she'll leave it to him. She starts explaining her escape plan, but
he has a much simpler plan – he just punches his way out.

In the camp, everybody's climbing ropes, except for Blob who can't pull
himself up. Scott and Lance start racing, get to the top, through pulleys,
then to rafts. Lance uses his power to make Scott fall into the water. The
other X-Men get angry and Spyke wants to sink Lance's boat, but Jean reminds
them that they agreed to not use their powers, and that Scott will handle
it. Scott proves her wrong, though, as he shoots at Lance's boat and wins.
The X-Men and the Brotherhood start arguing, as Pietro claims that Scott
slipped and Kurt tells him that he was avalanched. Everybody start shouting
at each other, but Sgt. Hawke breaks it up with his whistle. After they do
sixty push-ups each, Hawke decides to make it a team vs. team – first one to
get the flag from Mt. Humiliation wins, but it has to be the whole team –
Pietro racing there alone or Kurt teleporting there won't help. They need a
snapshot of the entire team on top. Scott and Lance start arguing and
eventually both agree to not use any powers. They leave to start at opposite
trails.

In Cerebro, Logan asks Xavier if he found any new mutant signs. Professor X
answers that there are only signs of the students in Ironback. Wolverine
says he still thinks he should have handled their survival training, and
Xavier answers that he gave them a choice - they felt they had a better
chance of surviving the camp. Suddenly, Cerebro starts beeping, saying that
there're new mutant signs matching an archive file, and then a picture of
Cain appears, much to Xavier's shock. He explains to Logan that it's his
half-brother, and that his mutant power was awakened with mysticism. He
became a Juggernaut, invulnerable.

In the camp, the X-Men are running to the mountains. Kitty suggests that
Kurt will teleport them to the top, but he tells her that they're not
allowed to use powers. The Brotherhood decided to skip their trail, and go
straight up – Toad hops, and Blob creates hold to climb on, with Pietro and
Lance tied to him.

Storm is in the X-Jet, and creates fog to hide her. In Cerebro, Professor X
is watching the news about the fog stopping the search for Juggernaut. He
telepathically tells Storm that she's doing very well and to keep it up.
Logan enters, and Xavier tells him that the only weapon against Cain is his
mind – psychic blasts can disable him, but only if he's not wearing his
helmet. Meanwhile, Juggernaut keeps walking down the road.

The Brotherhood reaches a ledge, and find an old mine. Toad checks for
shortcuts and finds that there's a tunnel inside that's like a stairway to
the top. Despite a 'KEEP OUT' sign, they enter. Meanwhile, Scott looks up
but can't spot the flag. The girls are still a little behind, so Scott tells
Kurt to teleport and check if the flag's still there. Kurt teleports
reluctantly, and tells them that the flag is still there, they're close and
no sign of the enemy. Scott tells Evan to fire a spike attached to a rope to
the top, and he does as told, after slight hesitation. Scott starts climbing
up the rope, but the others aren't too happy with cheating, and Jean starts
climbing the mountain. In the mine, the Brotherhood reaches the ladder, but
Avalanche gets furious at Toad because the hole is too small. Toad says he
could avalanche it open, and Quicksilver agrees. Avalanche starts shaking
the mine, and it collapses on them. The X-Men, who decided to climb up the
trail and not use the rope, feel the shaking as well. Evan falls, but Jean
catches him with her telekinesis. Scott says that it had to be Avalanche,
which means that the Brotherhood is close, and tells Jean to levitate them
to the top. She refuses, and just then Rogue finds the hole of the mine,
with the Brotherhood trapped inside. Toad begs them for help, and Scott
agrees.

In the Institute, Professor X explains to Wolverine that Cain's failed
relationship with their father, and his resentment of him, fueled his anger,
but after he was empowered, that anger became destructive and dangerous and
he had to be locked away. An alarm goes off, letting them know that he
arrived. Outside, Juggernaut is entering the Institute, with Mystique
standing behind him. Wolverine jumps on him, but he simply throws him away
and keeps walking. Wolverine tries again, and Cain tells him that he can't
defeat the Juggernaut, to which Logan replies that it won't stop him from
trying. They start battling, with Juggernaut winning, and the battle goes
indoors, with Mystique following. Cain keeps throwing Wolverine through more
rooms, and to Mystique's horror, Cerebro gets smashed in the process. She
gets angry at him, but he makes it clear that he doesn't make deals and
throws her aside, next to Xavier.

Back in Ironback, most of the Brotherhood is already out of the mine, and
Avalanche is the last to climb up. Pietro tries running to the flag, but
Kurt teleports there and they fight over it. The fight stops when the X-Jet
appears and Storm tells everyone that both Professor X and Mystique are in
danger. Scott and Lance agree to work together, and everybody take off. On a
trail, Sgt. Hawke watches the X-Jet flies by, as a picture floats to him,
showing the X-Men and the Brotherhood near the flag, with Blob and Rogue
holding it.

In the Institute, Cain has Xavier and Mystique against the wall, begging for
mercy. Xavier tries to convince him to end this differently, but he won't
listen, so the professor shouts a command to the mansion's computer that
makes it attack Juggernaut, but he easily defeats all defenses, from metal
arms to fire. Wolverine wakes up, but them he hears Cyclops and Avalanche
tell him to take a break – they'll take it from there. Mystique and Xavier
are both shocked to see their teams work together, and Logan tells them to
get the helmet off as Jean uses her telekinesis to take Cain away from his
brother. She faint in the process and Cain tries getting to her, but Blob
saves her. Nightcrawler manages to teleport and undo one of the helmet's
buckles before getting tossed away. Then Juggernaut goes for Blob and sends
him flying across the room. Cyclops tries attacking but it has no effect.
Avalanche manages to knock Juggernaut to him knees, which gives enough
distraction for Quicksilver to run and undo another buckle. Storm uses wind
to knock Juggernaut yet again, creating enough distraction for Shadowcat and
Rogue to phase through a wall and undo the two remaining buckles. Toad hops
on the wall and sends his long tongue to remove the helmet, giving Xavier a
chance for a mental blast, defeating him at last. Everybody cheer, and
Mystique comments that it's a rare sight. Xavier agrees and says that it's a
shame, but she disagrees, and walks away, calling the Brotherhood after her.
They leave, not before Avalanche actually tells Cyclops that as a group
leader, he's only half bad, to which Cyclops comments that next time, he'll
call the shots. Avalanche says that there won't be a next time, and they
leave.

In prison, Xavier puts Cain back in his place, and he and Logan go to make
the needed repairs on Cerebro. Scott tells Jean that it felt right to work
with the Brotherhood, and that it's a pity the Brotherhood won't do it
regularly.