Thomas was a petty thief for a large part of his adult life. He didn't harm anyone, he just took what he wanted and left. He was also a home intruder and would frequently use crowbars to aid in his thievery.
Late one night, he broke into the current residence of Christina Vandrudakis, the human vessel of Sabriel. Sabriel caught him by surprise with a camera flash and he accidentally knocked himself unconscious by hitting himself in the head with his own crowbar. Sabriel tied Tommy to a kitchen chair and decided to keep him as her personal plaything instead of reporting him to the police. She moved him down to the cellar tied his chair to the ceiling.
After thirteen hours, she returned to clean him as he had defecated in his pants. She then gave him four ounces of tap water. A few days later, she confides in him about her conquest of Hal Guelder. Upon realizing that he had no artistic ambitions, Sabriel decided to make Tom her first thrall. She revealed her Apocalyptic Form to him and gave him the power to invoke the Lore of Storms through laughter and transform into water.