The Case of the Unconquered Sisters — Todd Downing

An American family in Mexico hosts a group of archaeologists -- butis there an assassin among them? “Satisfactorily sinister . . . class-A sleuthing” (Saturday Review).
 
“Unconquered” is the family motto of the Faudrees, whose ancestor, a Confederate officer, fled to Mexico decades ago. Now his two granddaughters, Lucy and Monica, live there in a beautiful old house near some black lava fields. The fields have recently attracted a team of archaeologists from an American university, and they'll be the sisters' guests during their expedition to Pedregal.
 
But Lucy and Monica soon discover the visiting academics may be unearthing trouble: A professor has died. Strange and threatening letters have been sent. And oddly, owls seem to be invading. To dig up the truth about what's going on, the Faudree sisters will need some help from US Customs agent and amateur sleuth Hugh Rennert, in this tale featuring “good background, atmosphere and characters” (Kirkus Reviews, starred review).
 
“You won't go wrong in giving Todd Downing a try.” -- Michael Dirda, The Washington Post