A car breakdown in the pouring rain forces the three ??? - Justus, Peter and Bob - to seek refuge at Blackstone Castle. Lightning strikes the power line and shrouds the castle in darkness. The old walls make a ghostly impression. Count Gallagher, the lord of the castle, confirms this when he tells the three ??? that his castle is haunted: the figures on a centuries-old marble chess table move every night as if guided by a ghostly hand. But only one move at a time - an ingeniously thought-out chess move. The Count is obviously being challenged to a game. But why and by whom? The three detectives soon realise that there is much more at stake here than just a game of chess ...