Sam Guthrie was the son of mining foreman Thomas Guthrie born in Kentucky. He had to join his father to work in the mines, but one day he became claustrophobic and his mutants powers manifested. Sam blasted out, killing his father and most of the men on his crew. Afterwards, he was send to the Milbury Hospital where he would go on to meet Illyana Rasputin, Roberto Da Costa, and Rahne Sinclair; fellow mutants with their own dark past. They collectively believed that they were being trained to become X-Men, hence the strict supervision. Meanwhile Dr. Cecilia Reyes reminded them that they were considered dangerous and should not leave the Hospital until their powers were under control.
One day during a therapy session with Dr. Reyes they were joined by another fellow mutant Danielle Moonstar whose powers were unknown. Not long afterwards, Sam experienced a vision on which he relived the day of his accident. As days passed, the patients warmed up to each other and eventually the group came together when Illyana spikes Dr. Reyes' coffee with sleeping pills, allowing them to run amok on the grounds. Eventually the group discovered that Reyes had been lying to them and that the Essex Corporation planned on using them as mutant killers. They confronted Reyes, who trapped them inside force fields, but manifestation of Dani's mutant powers conjured the Demon Bear who killed Reyes and proceeded to hunt them. Eventually, Sam overcame his fears and along with Roberto aided Illyana in fighting off the Demon Bear until Dani got a hold of her powers and drove it away. As the sun rose, the New Mutants collected their belongings and Sam noticed that the force fields around the Hospital was no longer there. The group decided to head into the nearby town which Reyes had previously told them was twenty miles out. Not knowing whether she was telling the truth, they all decided to head out together; facing the unknown.