Lennox is described as being a "tall, rather loose-boned man", with a pleasant but weak face, and fair hair. His manner is "oddly apathetic". He is about thirty years old.
Lennox bears a resemblance to his siblings Raymond and Carol. However, Dr Gerard judges that he is of a less nervous temperament than Raymond and Carol. Lennox sits relaxed and limp, and Dr Gerard observes that he is exhausted with suffering. There is nothing physically wrong with him, but he has gone through mental suffering, and is now enduring dumbly. According to Carol, Lennox "hardly ever speaks now", and "goes about in a kind of daydream".
About four years before the events of the novel, Lennox snuck out of the house at night, and went into Fountain Springs to attend a dance. Mrs Boynton was furious about it. After that, she asked Nadine to come and stay with them. Lennox and Nadine fell in love, got married, and stayed on with the family.
Nadine asks Lennox to go away with her, so that they can live their own lives and have children, away from the influence of Mrs Boynton. Lennox says that they cannot leave, as they have no money, and will not be able to earn any, as they are untrained.
Nadine tells Lennox that it is a battle between her and Mrs Boynton, and asks him whose side he is on. He says that he is on Nadine's side, but that it is impossible for them to leave. When she says that she will leave him, he begs her not to, and tells her that he does not have the courage to leave his family.
On the afternoon of the murder, Lennox goes for a walk with other members of the Boynton family, Jefferson Cope, Sarah King, and Dr Gerard. He later returns to the camp on his own, and is seen by Lady Westholme and Miss Pierce. According to them, Lennox was walking like he was slightly dizzy at the time.
After Mrs Boynton's death, there is a change in Lennox. His apathy is gone, and his bearing is alert. Lennox tells Poirot that he returned to the camp and spoke to Mrs Boynton. He also set her wristwatch, and put it back on her wrist.
It is later revealed that on returning to the camp, Lennox had gone up to Mrs Boynton, intending to tell her that he was going away with Nadine. However, when he got there, she was already dead. He was in a state of shock, and mechanically put the wristwatch on her wrist.
At the end of the novel, Lennox is described as being a "sane, happy-looking Lennox with humorous eyes". He and Nadine, together with other members of the family, attend a production of Hamlet in which Ginevra is performing. It is revealed that Lennox and Nadine now have children.
Appointment with Death (1988 film)
In the 1988 film adaption of Appointment with Death, Lennox Boynton is portrayed by Nicholas Guest. In this adaptation, his circumstances are the same as in the original and the portrayal is fairly faithful in a few parts but where in the novel he is often morose and withdrawn, here he is slightly more engaged and upbeat, especially when his wife is not with Jefferson Cope. During the trip through Europe, he is often the one handling the camera, and taking snaps of Ginevra who likes her photo taken at the various sights. Later, on the ship from Trieste to Jaffa, Lennox actually has the energy to punch Jefferson Cope in the face when he discovers a cigarette case which he gave to Nadine. This fracas inadvertently saved Jefferson from an attempt by Mrs Boynton to poison him.
Appointment with Death (2008)
In the 2008 ITV adaption of Appointment with Death, Lennox is renamed Leonard and has a totally different backstory. Here he is unmarried and the son of Lord Boynton, the current husband of Lady Boynton. Leonard is therefore her stepson and like the other children of her family (who were all adopted), he detested her. He refuses to refer to her as "mother" or even "stepmother" as his father requested but insisted calling her "Lady Boynton". In this adaptation he does not live with Lady Boynton or the other children, who appear to stay in New York. Leonard stays in England and manages his father's house in Dorset while his father travels the Middle-east on various archaeological expeditions. Like Lord Boynton himself, Leonard is also a plausible suspect in the murder of Lady Boynton because he had remained behind working on the dig and did not go out for an excursion with the rest of the tour.
Leonard plays a major role in a sideplot. Towards the end of the show, a skull is found at Ain Musa and Lord Boynton actually believes it is the skull of John the Baptist which he had been searching for all his life. However, earlier on, Poirot had seen Leonard purchasing a bag from an Arab. Poirot found the bag hidden among some digging tools. Inside was a tooth with a gold filling. During the denouement, Poirot gives the tooth to Lord Boynton. The tooth fits the skull perfectly, showing that it is of recent origin. It turns out that the skull was planted by Leonard. He explains that all Lord Boynton had spent all his life "traipsing about the Middle East" conducting dig after dig but "time after time finding absolutely nothing of significance." Leonard said he wanted this to end and so he had planted the skull free his father "of this need". This ruse, although exposed, seems to have worked, as, at the end of the show, Lord Boynton declares that he is "cured of archaeology".