On her 15th birthday, Sentinels controlled by Onslaught destroyed her apartment, killing her parents and friends, and for weeks Hallie hid in the ruins of the city with several children she rescued. When Hallie went to seek help after Onslaught's defeat, she and all the children she was protecting were kidnapped by the mercenary group the Rat Pack and experimented on by the Rat Pack's employer, Arnim Zola. The other children died or were horribly mutated, but Hallie became faster, stronger, and gained the ability to throw bio-electric punches. She escaped and attempted to reach the Fantastic Four.