What happened to the ten days that, in 1582, Pope Gregorio XIII “stole” from humanity? Why is the 29th February 2000 a day that occurs only every four centuries? Was there ever a 30th February? What terrible secret is hidden behind the series of ritual murders that are devastating London and whose victims are only people born on the 29th February? Martin Mystère provides an answer to these questions, and also busies himself with revealing many other mysteries regarding our calendar.