It was a busy day on the heritage railway, with a large crowd of people turning out to see the visiting steam trains. "The clue just said that the final clue would be here but it didn't give any other hints", said Mike to Ellie, "so it must be somewhere obvious: somewhere where you'd see it if you were looking for it, but somewhere that you wouldn't otherwise notice it... Where would Turing have hidden it?" But Ellie wasn't listening. There was a brief gap in the crowds on the opposite platform, and she was busy looking at an intricate mosaic on the far platform wall.
"Excuse me", she said to a passing member of staff as a train pulled in, "has anyone ever noticed anything strange about that mosaic?" "Well", he replied, "it's been there since the station was refurbished in the late 1940s, back when I was a lad. My Dad told me that when it was put up, a rather eccentric character was very insistent about the design in the border being just right". "The border is exactly what I was looking at", she said, "And I think we've discovered what we were looking for".
The train was about ready to depart, and the platform was filling with smoke. As Ellie was copying the mosaic into her notebook, Mike saw Barbara and her two henchmen coming down the stairs at the far end of the platform. "Ellie!", he cried, "Quick! She's here and we have to leave - now!" There was no way off the platform, so all they could think to do was to jump aboard the train.
As the train pulled out of the station, Mike looked out of the window. "She isn't on the platform. She must have got onto the train as well. She's probably in the last coach, but she'll be looking for us. There's a lot of people on board, so it'll take her a while to get to the front. I hope we can solve the clue in time!"
What does the message say? The code word is the 12th word in the message.