Black As He's Painted (Roderick Alleyn Series #28)

Ng’ombwana is a (fictional) African nation to have emerged in the wake of colonialism; as it happens, its President is Inspector Alleyn’s old school chum, the "Boomer." Old school ties being what they are, the Boomer—making an official visit to London—insists that Alleyn handle his security, rather than Her Majesty’s Special Branch. The Special Branch is not best pleased about this, as the Boomer is known to have some very deadly enemies, and the threats only increase when the Ng’ombwanan ambassador is killed. Happily for the Boomer, not only is Alleyn up to the task, but he is assisted by the rescued cat Lucy Lockett, who may have lost her pocket but proves extremely adept at finding clues.