 Manning was deeply affected by the sudden death in 1977 of Jerry Slattery, her lover and confidant for more than a quarter of a century. Manning's last years were also made difficult by physical deterioration; arthritis increasingly affected her, leading to hip replacements in 1976 and in 1979 and she suffered poor health related to amoebic dysentery caught in the Middle East. Manning began work on the final novel in The Levant Trilogy, The Sum of Things, in which Harriet agrees to sail home to the UK, but having said goodbye to Guy, changes her mind. The novel describes Harriet's travels in Syria, Lebanon and Palestine, observes Guy's supposed widowerhood in Cairo after he hears of the sinking of Harriet's ship, and follows Simon Boulderstone's injury during the battle of El Alamein and recovery.
