This thinking challenge is one of the series of mysteries for students to solve either individually or as a group challenge. The clues are based on mathematical codes and ciphers and as each clue is solved it eliminates a number of suspects until there is just one possibility left. Answers are included. In my own teaching practice students are given the booklets to solve at the beginning of the week and I do not debrief with answers until three or four days later. This challenges the students to work on the puzzles at their own rate and to think about possible strategies. It also encourages collaboration. Each mystery includes a range of problem difficulty.