Arsenic and Old Puzzles

When an elderly boarder at a Bakerhaven bed-and-breakfast drops dead during afternoon tea, there's nothing particularly suspicious about it - except for the Sudoku in his jacket pocket. But when a second body turns up in the window seat and an autopsy shows both men were poisoned with elderberry wine, the Puzzle Lady suspects she's dealing with a cold-blooded killer who for some reason is copying the Cary Grant movie Arsenic and Old Lace, in which two old ladies who run a boarding house poison elderly widowers and bury them in the basement. More murders, more puzzles, and a grave dug in the cellar seem to cement the theory. Ordinarily, Cora would eat a case like this for breakfast, but for once she can't figure it out. And she's not sure if the clues don't add up, or if the much-married Puzzle Lady is just distracted by being involved in her first romantic entanglement in years.