Analysis: The biggest mystery, why pay for a story that's free?

The problem with the Byook is two-fold. Firstly, nearly all of its innovations - the raindrops spattering on the pages you are reading, the screams of the murder victim - are also distractions. Worse, they actually guide the reader towards the culprit.

Reading the story on the page, rather than on a smartphone, it is more open, less simple, more of a true mystery. This pappy app turns it into a melodrama.

Though the Byook doesn't modernise the words ("Mrs Hudson has been knocked up" merely means she has been woken early), it does inject an element of surprise to the text as when the page whitens before our eyes and we see the shadow of the murderer behind it.

But there's? a bigger drawback. A third of a way through the story, which has already cost 1.91, ends. To read any more, you have to part with 1.91 again. Why bother, when you can get read the story for free?