What are the motifs in Poirot Investigates by Agatha Christie?

Immorality surrounds most crimes in the story. The affairs of Gregory Rolf, Lord and Lady Yardly lead to blackmail and robberies. Immorality involves deception carried out by the servants that undertake robberies and murder. The moral characteristics that Poirot displays protects him at the same time from the temptation to do evil. Although it is his intelligence that gets him through various puzzles, his action is morally right and hence is rewarded in the end.