Claiming her true, non-biological self agrees to the mission, the Regulator persuades this sassy, outspoken vixen into becoming a host for him without protest, and promising her a magical, "biological" ability to transform her whole anatomy once the mission is over.
The problem? Well, apart from this entity that's controlling her making her look deranged for the entire Manchester to Croydon journey, Ruby hadn't contemplated what "stop" actually meant!
The Regulators have a job to do, Ruby almost gets that, especially after their agenda to help beings "pass the test" in the literal "game of life" we play for our true, eternal home, Omnipion, is explained. But killing a human, just because they may fail this spiritual test, really?
What happened to free will and all that malarky? Well, apparently one who's heading to "the point of no return", the lowest place in Omnipion one will drop if they commit enough evil acts during their collective lifetimes, can ask the Regulators to step in and help. Why? Because failing the test and becoming nothing more than energetic fuel wasn't something otherwise eternal beings anticipated. 
I mean, this Regulator may have given her a new outlook on life, even answered the question to the meaning of it, but killing some deranged man before he commits the heinous rape and murder of an innocent young mother, was something she could never allow... or could it?
Could she see things Omnipion's way, whose high-ranking beings deemed a human life as just one small test in the grand scheme of things, and end this potential murderer's life? Or will her aversion to this cold, otherworldly view stop the Regulator from carrying out its mission?
Well, she was certainly loud enough, even if just in her mind, to drive him out. But how sure was she about her own thoughts, with his in her head as well?
She could either let the Regulator use her body to kill this murderer, who she knows nothing about, and hence live with the guilt of them taking the law into their own hands, but get everything she's ever dreamt of, including the paranormal power to one day become pregnant and give birth. Or protest, evicting the Regulator from her body, and hence live with the guilt of setting the murderer free to kill some innocent young mother she could've helped save, and lose everything she'd dreamt of her whole life. Two choices she never thought she'd have to contemplate. 
The first was logically more sensible, but was it morally right to take the free will of a person before they've even committed the crime? 
Could trusting the murderers true self is the one who wants to end his life be enough to convince her? Would knowing how it saw what level of depravation his brain had dropped to and, therefore, what harm this sick, human self of his was about to cause to the innocent woman, and the devastation to her child, make all the difference?
Or, believing criminals think only for themselves, would Ruby see his higher self as doing a purely selfish thing? I mean, did his higher self only appeal to the Regulators, ordering them to step in and "stop" his human self for its own sake, so he wouldn't fail the test and become fuel for the evil being he was? Was he doing a good thing for the woman in question, or just saving his own eternal being? 
With the murderer ready to strike at any moment, and feeling the urgency of the Regulator whose dragging her body to him, there wasn't much time to mull it over. 
"THE HOST MEETS MINORITY REPORT"