Dumb Witness by Agatha Christie

When an elderly woman falls down the stairs and later dies under suspicious circumstances, Poirot is drawn in by a mysterious letter she sent before her death. Her family stands to gain from her will, but only her loyal dog, Bob, may have witnessed what truly happened. Poirot must unravel a case full of false assumptions, shifting alibis, and subtle cruelty. The plot is slow-burning, with a final twist that reveals how the smallest clues can point to murder. A clever case of greed, deception, and canine intuition.