According to Nurse Leatheran, Louise was not a Swede like her husband, "but she might have been as far as looks went". She had a "blonde Scandinavian fairness that you don't very often see". Her exact age was not given in the novel, but Nurse Leatheran judged her to be between thirty and forty years of age. Her face was rather haggard, and there was "some grey hair mingled with the fairness". She had lovely eyes, which were violet in colour, and very large, with faint shadows underneath them. She was very thin and fragile-looking. There was something "unearthly" about her appearance, and she looked "a fairy creature more than flesh and blood".
Louise was known as "Lovely Louise". Squadron Leader John said that this was taking her at her own valuation, as she thought she was lovely. However, Mrs Kelsey pointed out that many other people thought she was lovely as well. According to Nurse Leatheran, Louise was very lovely, and you could not help admiring her and wanting to do things for her.
When Nurse Leatheran first arrived at the expedition house at Tell Yarimjah, Louise took her around the house, and established her in her bedroom. Nurse Leatheran had formed the impression that Louise was a lady, and so was surprised when Louise cross-questioned her rather closely, as a lady does not display curiosity about one's private affairs. However, Louise seemed anxious to know everything about Nurse Leatheran, including where she had trained, what had brought her out to the East, and if she had ever been in America or had any relations there.
Prior to Nurse Leatheran's arrival, Louise had reported frightening incidents, such as fingers tapping on her window, a hand without an arm attached, and a yellow face pressed against the window, which was not there when she rushed to the window. A few days before Nurse Leatheran's arrival, they had been firing shots in the village, and Louise had jumped up and screamed.
On one occasion, when Louise and Nurse Leatheran were walking back to the house from the river, they saw a man in European clothes, who appeared to be trying to peer into the windows of the house. Louise was frightened until she saw him close up, and realised that he was an Iraqi.
On another occasion, Louise woke up in the night, and reported that there was someone in the room next to hers, and that she had heard him scratching on the wall.
The following day, Louise told Nurse Leatheran that she was afraid of being killed, and proceeded to explain why.
Louise had married a young man in one of the State departments in 1918, when she was twenty years old. She described herself as a "queer patriotic, enthusiastic girl", "full of idealism". When she had been married for a few months, she accidentally discovered that her husband, Frederick Bosner, was actually a spy on German pay. She reported him to her father, who was in the War Department.
Louise had believed that Frederick had been shot as a spy, until she became fond of another young man, and received an anonymous letter from Frederick, saying that if she ever married another man, he would kill her. She went to her father, who told her that Frederick had not been shot, and had escaped. However, he was involved in a train wreck a few weeks later, and his dead body was found amongst others.
Because the letter Louise had received opened up the possibility that Frederick might still be alive, her father investigated the matter carefully. He declared that as far as one could humanly be sure, the body that was buried as Frederick was Frederick, but there had been a certain amount of disfiguration, so that he could not speak with absolute certainty.
Whenever Louise became intimate with another man, she would receive a threatening letter. Three years before the events of the novel, she met Dr Leidner. She had not intended to marry him, but he made her change her mind. She waited for another threatening letter to arrive, but none did.
However, two days after their marriage, she received a threatening letter, and another came a month later. A few days after receiving the second letter, she and Dr Leidner had a narrow escape from death by gas poisoning, when someone entered their apartment while they were asleep, and turned on the gas. Fortunately, Louise woke up and smelled the gas in time.
Louise and Dr Leidner agreed that she should accompany him to Tell Yarimjah, and not return to America in the summer, but stay in London and Paris. She felt safe for a time, but three weeks before the events of the novel, she received another threatening letter with an Iraq stamp on it. One week before the events of the novel, she received another letter, which had been delivered by hand, and had not even gone through the post.
On the afternoon of her death, Louise went to her room to rest after lunch. Nurse Leatheran settled her in her room with her book. Later, when Dr Leidner entered the room to tell Louise that he had cleared some space on the roof, he found her lying in a heap by the bed. She was killed by a blow to the front of the head, just over the right temple, and Nurse Leatheran judged that she had been dead for at least an hour.
When Poirot investigates Louise's death, he feels that she is the hub of the case, and so asks the members of the expedition staff, as well as Sheila Reilly, about her. Sheila tells Poirot that Louise enjoyed drama, but did not want to be involved herself. She wanted to be on the outside pulling strings, and enjoyed stirring people up and setting them against each other. Sheila also says that Louise enjoyed finding out things about people, and holding it over, letting them know that she knew, and leaving them in doubt about what she was going to do. She also says that Louise had been having an affair with Richard Carey, and they used to meet outside. Louise would walk down to the river, and he would leave the dig for an hour at a time. Sheila believed that Louise really cared for Mr Carey.
David Emmott tells Poirot that Louise was like the Snow Queen in a fairy tale he read as a child, always taking little Kay for a ride. He says that she always wanted to be at the centre of things, and wanted people to turn their minds and souls inside out for her to look at.
From studying Louise's belongings, Poirot makes certain observations about her character. She was not a luxurious woman, and her tastes were simple, and even on the austere side. Some embroidery she was doing was of extreme finenesis and beauty, which indicated that she was a woman of fastidious and artistic taste.
From studying the books in Louise's bedroom, Poirot makes the observation that she had an interest in culture and modern science, and so she had a distinct intellectual side. Some of the novels she had seemed to indicate an interest or sympathy with the independent woman.
Poirot is convinced that Louise was a woman who essentially worshipped herself, and who enjoyed more than anything, a sense of power. He explains that such women naturally revolt against the idea of marriage. They may be attracted by men, but they prefer to belong to themselves. Poirot suggests that Louise may have believed that it was patriotism that led her to report her husband as a spy, but it may really have been an unacknowledged desire to get rid of her husband.
Poirot later explains that Louise was killed through the open window of her bedroom. She was lying on her bed, when the murderer dangled a mask at her window. This was the same mask which had previously been used to frighten her. When Louise stuck her head out of the window to see who was playing this trick on her, the murderer dropped a quern on her, killing her. The murderer later moved the body to a position by the bed, and switched the rug in front of the window with the one in front of the washstand.