Each alleged murderer had a motive for making sure Mr. Shaitana kept his or her secret, making any one of them the culprit. Furthermore, each of them had an equal opportunity to murder Mr. Shaitana. However, motive and determining who was most likely to execute the crime were irrelevant to exposing the murderer. Instead, the four sleuths, Hercule Poirot included, had to learn who had enough gall to kill Mr. Shaitana while three other bridge players in close proximity vied for a wining hand. Determining who bore that psychological composition required delving into the incriminating pasts of each alleged criminal. The inquiries revealed stunning revelations, plus characteristics that made each suspect more likely to have murdered again.
Overall, the plot carries enough plot and suspense to keep readers guessing who murdered Mr. Shaitana. More than ever, Christie explored human psychology to illustrate how crimes are committed in a similar fashion.