Oh my ... so, this john gets himself a prostitute with the intention to drug, torture and kill her. Still, he is so unprepared, that he doesn't expect the driver (to whom he had explained the way to his place just about an hour ago). Then, he, the terrible successful serial killer LISK messes up the drug dosage so she is able to come back (we leave here out, why he didn't restrain her in the first place, because that is usually the next step after drugging to subdue). Oookay, lets say, I don't buy it because it's already somewhere between unlikely and bad novel up till this point.
But it goes on. John asks the driver in. The driver is some kind of career criminal, who is in this business for years. He would recognize that someone drugged the girl or at least that she was drugged. And he would know, she wasn't when she went in. And of course, he would also see the difference between drugs used to subdue someone and drugs for "recreational" purposes. Unless SG had a habit to take sleeping pills for recreational use ... oh well.
And the thing with the phone call, I love it. The operator reports of a pretty exited caller, exited in the negative sense. Loud, screaming "they want to kill me". Surely the picture of someone who was sent to sleep by drugs to subdue said person. And they let it go on for 23 minutes. Wait ... they ... because our homicidal john had his friend the drifter there. Ok, to speak with Cannel: "Castle, you lost me here!" I mean, very rarely SKs invite friends over to have more witnesses.
Lets say, this theory doesn't look too convincing to me. Maybe it needs more detail work?
Peter