The cover text reads:

Can You Crack The Code?

Edith Twyford was once a world-famous children's author, but now her only legacy is the rumoured existence of the Twyford Code: a series of clues hidden in her books leading to . . . what? No one knows -- but that hasn't stopped the speculation.

Steve Smith can trace nearly all the bad things in his life back to Edith Twyford. As a child he found one of her books, covered in strange symbols. He showed it to his teacher, Miss Iles, who was convinced it held the key to the code. Within weeks Miss Iles had disappeared, and Steve has no idea if she is dead or alive -- or if she was right. Now he's determined to find out.

But the Twyford Code hides secrets some would do anything to possess, and Steve isn't the only one looking.

The race is on to solve the mystery of the century.
Can you get there first?

The story unfolds as a series of incomplete and garbled transcripts of audio files recorded on a mobile phone. They are incoherent because the automatic transcription software has substituted similar sounding words for things said in a local accent. The phone is believed to have belonged to Steve, a minor London criminal, and now a missing person.

This was just one of those random books that caught my eye at the bookshop. The audio files jump around in time, making the story a bit convoluted, but you just have to know whether Steve finally solves the Twyford Code or stumbles into something darker.

left in The North End pub (which has more Irish beers than English since Brexit)

Found in North End (pub in Leiden) on 21 september