Rennie Airth said this quote

“ There was something about the story she told us...that didn't seem right to him. He didn't buy the idea they'd been lovers. He reckoned it was something else. It's the sort of thing he used to pick up on, when I worked with him. You know as well as I do, sir, in a case like this you collect all sorts of facts, but only a few really matter, and Mr Madden had a gift for spotting them. Not that he always knew why: often it was just something he felt - a sort of instinct, I suppose - though he would have said it was simply a matter of paying attention. That's what he used to tell me. ”