Helen awaits trial in a crumbling women's prison in Southampton. She has a fight on to prove her innocence from inside her prison cell, but this soon turns out to be the least of her worries. A serial killer is picking off fellow inmates, thriving in an environment where there is truly nowhere to run. Is it a criminal giving in to their dark urges or a member of the prison staff preying on the captive population? Helen must work fast to reveal this devious killer, all the time wondering if she will be next on her list . . .