In "A Fisher of Men" in Dr. Thorndyke's Case-Book by R. Austin Freeman, Thorndyke was talking about a man who went to visit another one who wants to buy his expensive necklace, saying:
"Mr. Montague's destination was Isleworth, in which rather unlikely neighbourhood Mr. Jacob Lowenstein, late of Chicago, and now of Berkeley Square, has a sort of river-side villa with a motor boat-house attached. Lowenstein had secured the option of purchasing the blue diamond necklace, and Montague was taking it down to exhibit it and carry out the deal."
I know the meaning of "unlikely" itself, but I can't see its meaning in this context! Does it mean "remote" or "strange"?
And what is meant by "secured the option"?