The quiet town of Granville is shocked by the mysterious murder of Professor Avondale, the founder of a unique museum of puzzles. However, who and why needed to kill a harmless old scientist? Sheriff Brandon Mitchell, who recently settled in Granville, considers the main suspect the favorite student and the only heir of the professor, Kate MacDonald. Kate understands that in order to prove her innocence, she will have to find the real criminal. But this will not be easy, because the killer did not leave any evidence. Perhaps, in order to solve the mystery of the professor’s death, Kate needs to deal with Sudoku - the puzzle whose cells he filled in before his death? ..