Superintendent Battle is in charge of the investigation by the police. He agrees to work with the three other sleuths, unusual for the police, sharing all facts equally. He says in Chapter 19, "Cards on the table, that's the motto for this business." There is a theme of playing cards in the plot, as the potential murderers played a card game, contract bridge, as the murder was committed, and the manner of playing bridge (level of skill, risk taking) is part of Poirot's way to study the psychology of each individual.
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