Walter Huff
Walter Huff is a conscientious insurance agent who works hard and sees success because of his hard work. He is well respected at work and has not put a foot wrong his entire career. The events of the novel unfold largely because he is a hard worker, and wants to generate more business; he visits the Nirdlinger home because he wants to persuade Mr Nirdlinger to renew his automobile insurance. He finds himself instantly captivated by Mr Nirdingler's wife, Phyllis, even though he almost immediately realizes that there is something forbidden and dangerous about her. When he senses danger coming, he chooses to stay and talk rather than leaving, and this is when his life changes from propriety to crime.
Walter has a strong streak of self-preservation which he demonstrates by creating an airtight alibi for himself and making sure that there is nothing to connect him to either Phyllis or the murder. During the period of time between the murder, and its aftermath, he finds himself falling in love with Nirdlinger's daughter Lola, who has come to him for help, and who is hugely suspicious of her step mother. This turns out to be one-sided; Lola has a boyfriend whom she soon marries. His self-preservation streak is demonstrated further when he makes a deal to turn on Phyllis in return for a new life in Mexico.
At the end of the novella Walter realizes that he has ruined his life; he has no home, no work, no insurance business, no loved ones and no future. This causes him to commit suicide by jumping from the ship to Mexico.
Phyllis Nirdlinger
Phyllis is a femme fatale character at best, and a black widow at worst; she seems sociopathic and no conscience to speak of. Some of her decisions seem downright depraved, for example, asking Lola to be a witness at the signing of the insurance policy that is the catalyst for her father's murder. Phyllis is very attractive and knows how to use her alluring looks to manipulate men into doing whatever it is that she wants them to do. Phyllis has most likely already killed at least once before; she used to be Lola's mother's nurse, when she was suffering from pneumonia, and although her death was said to be from the disease, Lola believes that her mother was murdered by Phyllis with the sole objective of becoming the second Mrs Nirdlinger. Phyllis believes she has come up with a perfect murder, but when she realizes that she has not, and that she is likely going to be arrested once the ship docks in Mexico, decides that suicide is the only answer for her.
Lola Nirdlinger
Lola has been the victim of Phyllis Nirdlinger twice, first when Phyllis murdered her mother and then when she murders her father for the insurance money. Lola does not like her stepmother and is suspicious of her, determining to see her in court and punished for her father's murder. She does not seem to have any idea that Walter is involved and in fact uses him as a confidante of sorts, which Walter mis-reads as a romantic connection. Lola in fact is in a committed relationship and marries her boyfriend shortly after her father is murdered.
Barton Keyes
Keyes is the senior claims manager at the insurance company where Walter works. He has previously liked Walter but he is immediately suspicious of the insurance claim filed by Phyllis Nirdlinger, and his suspicions mount more when he realizes there is a prior relationship between Phyllis and Walter. Because he likes Walter he gives him the opportunity to be the one who "rolls" on the other, and is instrumental in offering him a deal. Keyes is a smart man who can smell a rat very quickly and who is not going to let any insurance schemes succeed on his watch at the company.
