The accounts balanced except for one small triangle beside every Thursday total. Iris found no explanation in the café's sale papers. The previous owner was dead, and his executor suggested that the mark probably meant cash taken home.
Iris copied the entries into a spreadsheet. The triangles appeared even on Thursdays when the café had been closed by flooding. They could not describe sales. On one page, the pencil had pressed hard enough to leave the same shape on a scrap used as a bookmark.
The scrap was a bus timetable. Thursday's last service carried the owner's sister back from treatment. A former waitress remembered that he marked the ledger when someone had walked her from the stop. On flooded evenings, the café stayed dark but the collection still happened.
Iris kept the old ledger beside her own. She did not adopt the triangles; a private code should not become a decoration. Instead, she added the waitress's explanation on a separate sheet, so the next person opening the book would find an answer before inventing an accusation.