The Lively Dead

In this mystery from CWA Gold Dagger winner Peter Dickinson, a landlady discovers a corpse beneath her crowded London boardinghouse

A sturdy young woman with a knack for home repair and a practical sense of Marxism, Lydia is renovating her London townhouse while her husband finishes law school. To bring in extra money, she rents her upper floors to the exiled government  of Livonia, a Baltic state that was long ago absorbed into the Soviet Union.
 
One day, as Lydia is taking up the floorboards, the Livonians carry a coffin through the house. It bears their housekeeper, who is to be honored with vodka toasts and a solemn funeral. After the ceremony, Lydia returns to her floorboards. Beneath the rotted wood is dirt—and in the dirt, she discovers a corpse that never reached the graveyard.
 
Identifying the body and finding the person who stashed it there draws Lydia into a tangle of spies and counterspies as her quiet little boardinghouse becomes a new front in the global Cold War.