This is a poorly written, illogical plot. That said, it may show the truth about how a police force actually works. Don't they have any semi-competent solicitors in the UK? Is that the way the accused/witness interview process works? Watch it to see how things don’t make sense. Essentially, it is about a poorly written and unsympathetic character/lunatic, who happens to be a police detective. BTW, she's no Sherlock Holmes in any sense,