You approach it with a preconceived theory to which you are determined to adhere.

Your theory is plausible and convincing--to some extent--but that is all the more reason why you should examine and test every link in the chain.

You cannot solve difficult points by ignoring them and, to my mind, there are some difficult and perplexing features about this case which do not altogether fit in with your theory." "If my mind is an open book to you perhaps you'll tell me what my theory is," responded Superintendent Galloway, sourly.
"Yes; that's a fair challenge." The detective pushed back his chair, and stood with his back against the mantelpiece, with a cigar in his mouth.
"Your theory in this case is that chance and opportunity have made the crime and the criminal.

Chance brings this young man Ronald to this lonely Norfolk inn, and sees to it that he is allowed to remain when the landlord wants to turn him away.

Chance throws him into the society of a man of culture and education, who is only too glad of the opportunity of relieving the tedium of his surroundings in this rough uncultivated place by passing a few hours in the companionship of a man of his own rank of life.