Before joining Torchwood, Tosh was working in a government defense building, but was really trying to access blue prints they had for a sonic device (this was five years before the show began) that would severely harm human hearing, causing anyone who heard the noise to feel tremendous pain. She stole the blueprints for the design and took them home and built the device. She then took the device to a man and a woman, revealing to the viewers that her mother had been kidnapped and she had been forced to build the device. She hands the device over to the woman, and her mother is brought into the room. The woman and the man put on ear muffs, and the woman activates the sonic device, causing Tosh and her mother immense pain. Luckily the area is raided by UNIT
troops, but Tosh is then arrested by them.
She is then put in a cell (in a red jump suit), containing nothing but herself and a device on the ceiling which she was able to ask questions too, and that also gives her updates of sorts. One day, she is visited by Captain Jack Harkness
. He takes her out of the cell, and talks to her. He explains about how she is most probably going to rot in her cell for the rest of her life, but he has a way out for her. He tells her that the blueprints for the sonic device that she stole was wrong, and have several flaws in it, but she instinctively fixed them, and that is what he needs for his team.