Does Dan Brown's new novel dish the dirt on Walmart?

I only ask because on Saturday the selling of the book in Asda was very cloak and dagger!  I had to go to town for a hair appointment and I saw the book in the local book shop half price.  I could have got it there but I thought it will be a tiny bit cheaper in Asda and it will be nearer to the car. So in Asda I checked the book section expecting to see this newly released tome in pride of place, but no sign of it.  So I got groceries and paid then as I was passing the customer service desk on the way out there was a copy of the book standing in a strange display. "So you do have the book" I exclaimed, and the woman behind the desk said "Yes I have some under the desk, would you like one?", "How much are they?", "£5" (that is quarter price!!!!!), "Yes Please!". I was told they were more expensive when they came in too.

So I am now the happy owner of a real bargain, but why are the books hidden?