Written by Agatha Christie
Copyright 1929
[Edgar Wallace general style] "At Inspector Marriot’s behest, Tommy and Tuppence sleuth after a clever counterfeiter who has been flooding both sides of the Channel with phoney bank notes. Tommy winds up in an alley with chalked X’s over the doors – but what do they all mean?"10th story in the collection Partners In Crime.
Here are the pages I have of it.