Beth Childs was a police detective, partnered with Arthur Bell and living with her boyfriend, Paul Dierden. She was also intensely depressed, paranoid, and medicating on pills as she navigated the quagmire that composed Projects Leda and Castor, the Proletheans, and Neolution. The show actually begins with Sarah Manning seeing Beth commit suicide by jumping off a platform in front of a moving train. In the last second before she jumps, she looks directly at Sarah, who is shocked to see her own face staring back at her.
What a way to begin a series, huh?